This is something that I've seen Japanese writers (in Manga/Anime) do especially well. From what I've seen there, I'd say...

The key to pulling this off is in how your MC reacts to her jealous feelings.

If she gets petty and takes it out on her love interest (as you describe with pouts and annoyance), it may be seen as obnoxious and non-productive by your readers. This trait is only holding back their romance and nothing but selfish/annoying. Would you want to date someone who gets mad at you for reasons outside your control (like with the waitress)?

However, if she uses this jealousy to push herself to try things outside of what she would normally do to "compete" with these other girls (who--to the reader--clearly aren't actually competition), it'll come off as endearing. She's trying hard to win her love interest, and "fight off" the competition. It would look like a small dog trying to defend its owner from a huge Boxer, when the Boxer is just walking past them.

You can also play this up with the self-esteem issues. "I'm clearly not beautiful/interesting/intelligent/etc. enough for my love interest, so to compete with these other girls I'll have to XYZ."

You can further give this a cute spin by making it clear to the reader (but maybe not the MC) that the love interest clearly finds this all endearing and is trying to play along to help her save face.

And the beauty of all of this is that she'll be trying so hard to step outside of her comfort zone for the love interest that she won't be able to keep it up forever. While this may start as cute and endearing, it's probably taking a toll on her. Combined with the self-esteem issues she'll probably be thinking along the lines of "I've been trying all of this and failing miserably. Does [love interest] even like me?" And when she finally breaks, it'll setup for a beautiful scene between them where the love interest can "give back" emotionally and express their feelings for her (which would also give you a great point to start chipping away at those self-esteem issues!)

One way that I have seen in real life is the combination of self-awareness and levity. It is important that self-awareness happens in the moment. Many people realize too late that they had done something stupid out of jealousy. An example might look like this:

How can you just go get coffee with him?

What do you mean, him? I get coffee with co-workers almost every day. Why does it matter today?

Because look at him. His big arms. Chiseled chest and abs. Look at his skin. It's perfect. Okay. I'm starting to think that you should be the one who's jealous here.

Me too!

I'm gonna go get some coffee. See ya later.

This isn't something that has a high re-usability rate though. This will go from cute to annoying with prolonged use, although that can be said about a lot of things that are cute. I would also think you are setting up a character to later cross a line if they have reoccurring jealousy issues.

Jealousy isn't, and shouldn't be seen as, a cute trait. Is it human? Understandable? Absolutely. But make no mistake, the possessiveness of your fellow man, no matter how understandable, isn't a 'cute point'. It's a flaw.

And that's fine; treat it as a character flaw. There's nothing wrong with this, in fact, generally it gives characters depth. I think it's better to include the jealousy and treat it as a flaw than include jealousy and give the character a 'free pass'.

Acknowledging that the top answer cautions controlling another person is abuse, and abuse is never cute, I'll try to suggest ways to minimize the issues.

• Avoid Blame: The lover is not at fault and clearly not doing anything wrong. The protagonist can see this, and trusts the lover,
  but can't help having emotions about it. (Cue regular intervals with
  a therapist.)




• Self-Deprecating: Woody Allen (yikes!) made a career out of self-deprecating comedy. It worked for his neurotic characters,
  especially since many of his jokes seem like
  inner-monolog/commentary. The problems with using Woody Allen as an
  example is that his co-stars were extremely attractive women, and
  there's an undercurrent of real abuse and gaslighting sprinkled in to
  show that Allen's neurotic characters are not the victims they
  portray themselves to be. A particular line in Manhattan sets up
  a joke where Allen's character had followed Meryl Streep (his ex) on dates with
  her new girlfriend in his car, but the joke turns dark when she
  corrects the story by saying he tried to kill them with his car.




• The Lover is an extremely secure person: the protagonist is allowed to be unreasonably jealous because the lover is unreasonably
  self-secure. They are a Rock of Gibraltar. No amount of commentary or
  jealousy will change how the lover feels or behaves. For this to feel
  real there would probably be a power difference between the 2
  characters, like Woody Allen being involved with supermodels, or
  typical of 1950s comedies the jealous person has essentially no power
  in the relationship so their antics are reduced to hiding in bushes
  to overhear, and attempts to become sexier or more interesting that
  come off as strange or funny rather than sad and desperate.




• Punch up, not down: This goes for comedy in general, so how to apply it here? The jealous one is wealthy beautiful and successful.
  The lover is plain, simple, and domestic. Again it uses an
  unrealistic power difference to take away the stakes. Another way to
  do it is to make the point of jealousy the one thing the perfect
  character doesn't do well, like cook. It's sort of a trope reversal
  on the Woody Allen character where the neurotic is such a
  perfectionist at all things that the jealousy is over something that
  should be trivial, like the husband complimenting another woman's
  rhubarb pie, so the perfectionist becomes obsessed with baking (and
  failing) to win back her lover's attention through deserts.




• It's their job: the lover's job is that he plays a Casanova on television, or she's promoted as a "love goddess" like Marilyn Monroe. The truth is they are homebodies, lovingly faithful, and painfully shy, but of course as actors they can't disappoint their fans and must the play the role in public appearances and publicity "scandals". The jealous one's rival is abstract, it's the job and the fame that creates the tension, and again the lover is not at fault.




• Don't dwell on it: A small outburst is like a yelp of pain – sometimes we cry out before we realize we're not actually hurt. Let
  the jealous one object, but then retract when they realize they are
  probably over-reacting. It can look cute because it's like showing
  their cards too early in the relationship. They are already signaling
  how they feel when the situation suggests they should be playing it
  more casually.

Why this is difficult.

Jealousy is a natural trait, nearly everyone that falls in love is subject to it at some time. The reason is that the extremely high emotional value of the love interest creates all sorts of effects. Obsessive thinking about them, extreme focus on minor clues of behavior or particular words, cravings for constant contact (holding hands, sitting together touching, arms around each other, frequent kissing, and of course more intimate touching and intercourse).

The negative side of this extremely high emotional value is the fear of loss, and thus a fear of competition, and obsessing on every detail of interaction that might remotely suggest your love interest has any other interest, or any other person might have interest in them.

Jealousy is a form of personal insecurity combined with an active mistrust of the love partner. (Sometimes this is warranted, love can be one-sided and partners may stray.)

It is mistrust to believe they are weak-willed and so selfishly impulsive and superficial they will drop you or cheat on you for a quick lay with someone else, or might even drop you for that.

It is personal insecurity to think your love is not reciprocated, that you are not good enough to hold your partner's interest. This implies they have little commitment and only love you for superficial reasons they can readily find elsewhere; that your qualities are just commodities and your partner is always shopping for a better value -- Somebody funnier, or smarter, or sexier, or kinkier in bed.

This is why it is very difficult to make actual jealousy "cute", it is a manifestation of mistrust and insecurity. And although both may be warranted, when they are not the expressions of mistrust may itself ruin the relationship, no matter how cute you make them. Being mistrusted often results in reciprocation of that mistrust, and mutual distrust breaks the love spell.

Jealousy does occur in most love connections. IMO the best way to handle it is NOT to express it directly, but to have the character struggle with it and find a way to deal with it, to realize their mistrust will ruin them. Perhaps channel it into something else romantic, to reaffirm to themselves they trust their partner and their partner loves them.

How to Represent Jealousy in a Cute Way

In other words, have a self-aware character that understands the stakes and won't surrender to jealousy. It is a conflict they must overcome, which is great for fiction, conflict keeps the reader turning pages. And battling this internal enemy, without revealing their mistrust to their love interest, is something you can do in a cute way. Show their self-talk and self-affirmations, dealing with their insecurities, examination of their own motives and exaggerations of their "competition". People in love are very skewed by their obsession, thus illogical, and that can be funny and recognizable and relatable.

But in the end, I wouldn't express jealousy to the partner. You might get a laugh out of it. In real life relationships people in love get over it, all the time, because forgiveness for an overreaction is something given when in love. But there is a limit, constant jealousy (mistrust and insecurity) is a poison to a love relationship, and can make the mistrusted person feel like a property controlled by the jealous party. That stops feeling like mutual love, and is a recipe for falling out of love.

Let's back into what "cute" jealousy would look like. Inspecting the other answers, a common theme is that jealousy is a step towards potential abuse, or it is simply poison to a love-relationship. Jealousy carries undertones of distrust, perhaps even malice. Or, to offer a slight oversimplification, jealousy isn't cute because it's threatening.

The problem, therefore, with portraying jealousy which is cute would be to make it not threatening. Unthreatening jealousy is actually not strange or unusual, but it's main manifestation is not in romantic relations:

"But Daddy, why didn't you take ME out to get ice cream?"

"Timmy, you know it's Cindy's birthday. On your last birthday, we
went and got you a banana split. Remember?"

Relatively "innocent" jealousy is not an unnatural state. A child (or childlike character) who is not inclined toward malice may still be disappointed to be left out, may still feel soft envy, without being overwhelmed by hostility or distrust.

The problem with putting that kind of character into a (plausible, mature) romance is that either your "cutely" jealous character is on unequal footing with the mature other character - or both of your characters are not really emotionally steady enough to be actually devoted to each other in a healthy way. I suppose this would give them room to grow.

"I'm sorry, doing things with friends having an attractiveness rating higher than 50% will incur floral penalties. With Kelly? I'm thinking calla lilies..."
"Higher than 60% Oh dear, now we're taking backrub. And a loong one, my darling!"

While I don't find jealousy cute, the idea of two people coming to an understanding allowing one to "transgress" in this way by paying penalties of flowers or cooking or backrubs, or bubble baths together or whatever, makes sure that the couple has a fun interaction of their own. I can see that as helping to strengthen the relationship and add fun, so that they don't wind up with "fun is for friends, my beloved is just a participant in our daily routines" kinds of effects.

As some answers have said, jealously isn't actually "cute" at all. If you're thinking about "cute portrayals of jealousy", the odds are good that you are actually in reality thinking of some other emotion, not jealousy.

So I don't think this question can be answered as asked, without considering what exactly it is, you want to portray.

First thing first: I'm Italian, and my English will probably fail. I say this because this is "writing" stackexchange, and I know who's writing is pays a lot of attention to good sentences and grammar, I do exactly the same in my native language :)

Having said that, I remember once I've read Chaplin speaking about how he do funny scenes, I've tried searching on google for the exact sentence but I'm unable to find it again. Anyway, he said that a character doing a mess on screen is funny but what's even funnier the effort he put into trying to hide it and look like a perfect gentleman.

In the case you describe, I would put this jealousy into this girl who perfectly knows she can't show it, because she's a mature well educated girl or just because she don't want to show her weakness, anyway this repression could lead into any funny situation, she could stumble into anything, or confuse words speaking to him.. the main point is that, as you've seen from other answers, jealousy It's such a slippery slope, easy to turn it into something painful (because she thinks he's somewhat not in love or not as much as she is maybe), but one point is sure: we're all jealous despite what people try to think, and we all know jealousy can go wrong. I think a scene where she knows all that so she tries to hide it could result in a very funny situation!

Maybe something simple like a motion such as pushing up her glasses, buttoning the top button of a shirt, letting her hair drop to cover her face on the side nearest him. She does it to symbolize her distancing herself or trying to ignore what she sees. But he sees it as a habit that endears her to him. Perhaps he doesn't even put the two things together if she does something different every time, but these little quirky subtle actions are what draws him to her. The things he finds irresistible that no one else does and helps him realize she is the only one for him.

Care would need to be taken to tell the inner monologue of the flirter immediately afterword to catch their perspective of the quirky behavior.

There are so many good answers here. The scenario you are trying to figure out is really a key point to the readers and jealous here makes it even more difficult for author to explain this scene. Myself, I thought of a line which may help you. The main character says:
"Seems like I have to take the responsibility of protecting you like a treasure from the rest of beauties" or something similar.
It is like saying that he is her's treasure and she feels jealous and anxiety whenever someone tries to steal him. I don't think it is excessive as possessive.
It also depends on how the other character takes that. I will be great if you explain his feelings too, for justification of the main character's worries.
I find it as a cute way to express jealous, Thanks.

Make the person in question a cute girl.

There have been scientific studies that have shown that people are generally more positively-inclined towards women (dubbed the "women are wonderful" effect), and that people generally perceive physically attractive people in more positive ways, even in areas like perceptions of morality where physical attractiveness shouldn't matter (which is called the "halo effect").

Combine the two of them together, and you've got a recipe to cause your readers to subconsciously overlook a lot of the negative traits of the character.