Aot Headcanons

Jealous

Eren
As I said in the first chapter, you made a lot of friends in the training camp. So it's only natural for him to feel the jealousy bubble up when someone steals you away for a moment. He knows that you are a kind person and anyone could fall for that little smile you give your friends when they walk by.
He also does not deal with jealousy well at all. He will complain to you about the person who stole you away for a moment right when you come back.

Hear me out here, you will hate me. But if you wear something nice and revealing and someone makes a comment, he will ask you to change it (i have a feeling that something like that has actually happened in the show)
So in conclusion jealousy is not something he is good at dealing with
But I will throw the dog a bone and say that he will apologise for asking you to change your clothes.

Mikasa
Oh dear god this hot psycho
She is always behind you, she watches you like a hawk. May the lord help that poor guy who flirts with you and then finds out that you are dating Mikasa, he will not survive out of it without a good scare and 5 years of full time therapy.
Like that one time Historia just talked to Eren and she just could not stand it, that happens every time you dare to talk to someone without her there.
I feel cringe even writing this, like we are dancing on the line of some yandere shit and I don't like that.

Cat Callers die, she will hurt them.

Armin
So here I imagine that Jean would hold his arm over your shoulders. You have been friends since childhood, he doesn't think anything of it, you are just friends it means nothing to him. Armin finds this a little annoying most of the time it happens, since he is the one who should be like that with you. How does he deal with it? Well he does what you would think anyone does, tells you that it bugs him and you mention it to Jean who was surprised and didn't even realize what he was doing.
If Jean ever does it again out of old habit without thinking and even you don't notice he will wait till it happens again before making any bigger deal about it than it is.
If someone catcalls you he will just make sure you are okay, maybe give the guy a bad look if it was something really nasty.
His pretty cool about it and can separate the truth from what his feeling most of the time

Jean
He is a pretty protective guy. Like if he hears someone talking about you and saying or claiming nasty things about you, he will start a fight.
He will get jealous pretty easily as we have seen with Mikasa and Eren. He also does not take it that well because for some reason starting a fight (usually it stays verbal) is always the best option with this guy.
If someone is flirting with you he will throw an arm around your shoulder to signal that the two of you are dating and that the other guy should back the hell away. If that doesn't work he will straight up tell the other guy to go fuck himself and stop trying to get you to do it.
So in short he is really also very bad at dealing with his emotions.

I do feel like I should mention that between seasons 3 and 4 he does mature a lot so after that he becomes less physical, maybe an insult or two sent to the other guy's way before just helping you out of the situation and making sure you are fine.

Catcalling is something he can't stand at all. It's such a rude thing that makes women at the worst feel threatened for just walking down the street. He will say some choice words to the harasser, hoping they will learn their lesson .

Connie
I'm really not sure. I most likely feel like he is not a jealous person at all. Like he sees good in people most of the time and tends to give them the benefit of the doubt. If someone says that they see you as a friend he will believe them because why would they lie.
Sadly none of us are 100% immune to jealousy. When he does get it he will basically make that person seem like a clown, he turns from a comedian to an insult comedian. Always behind their back though because this twinkle noodle doesn't wanna die. (i'll take it seriously now)