I get jealous easy by virtue of being a possessive and overprotective person in general.
Overall I'm more a Violently Overprotective Girlfriend type than anything else. I'll get really Ax Crazy really fast if someone I love is put into any sort of danger by someone. And depending on what I have access to at the time will determine how much pain I'm going to put you through.
I have slight Yandere tendencies though, I admit. Not enough to get psycho just over jealousy, but I hope no girl is ever suicidal enough to start coming onto my man (you know, if I had one) and then I find out about it. I tend to do very irrational things when I fly into a fit of rage, and something like that would certainly send my sanity overboard.
Although if it's one of his friends and she's not trying to steal him for me, then I'll only keep an eye on her. You know, instead of giving her a death glare every time I see her.
If it's some random chick on the street then I'm gluing myself to his side and will likely break the rule have against PDA. And break it a lot.
To the point though, I'm insecure and I know that. However, it's not that I wouldn't trust him or anything, nope not at all, it's that it's not him I'm worried about - it's the ****es, ****s, ****s, and ****s I don't trust. To me it's not a matter of trusting him, if I'm romantically involved with anyone then I trust them **** tons more than I do everyone else, it's a matter of not being able to trust other women who are interested in him. I can trust him to keep his hands off of them, but I can't trust them to keep their hands - or eyes - off of him. Esp. if I'm right there and they still have the arrogance to flirt with him or something of the sort. Because it means they don't even ****ing acknowledge I could potentially be his girlfriend.
In short, I've got issues and I know this. So I'm gonna have to eventually find a guy who doesn't mind a possessive girlfriend. Not the ruin-your-life or isolate-you-from-everyone type though, no, just possessive enough to make it clear to anyone and everyone that if you try to take who or what is mine then I'll cut you... a lot...
Should be noted he can also be possessive of me in the same manner, I don't mind, I actually rather like the notion of having someone like that. But in my case it would be rather pointless since I reject anything with a Y chromosome anyway... and any BF I get would just be that weird-**** anomaly that pops up once in a while. Still, if he ever caught some guy checking me out (laughable as that notion is) then I wouldn't mind him getting jealous and possessive, making it clear that I was his and whatnot.
So long as it doesn't end up in a physical fight, unless the third party instigates it, then it's all fine by me. I'm not gonna smack some **** who was checking him out or anything, I'd more likely grab him and kiss him to make my claim on him known to anyone who might be getting any ideas. Now if I do this and she still tries something... then it might get physical. Depends on what she does.
Long story short, I'm possessive, a little crazy, and way overprotective. And I'm cool with that. I'm not gonna hurt anyone or anything, unless they try something stupid, so I see nothing wring with it. But there are many variables to consider regardless, I may not end up acting this way depending on the relationship and the guy and the types of girls he interacts with. Just depends.