So this guy was okay before...I mean I could tolerate him. But lately he has been intolerable. He threw his best friend's things in a tree and stole my purse, is starting to swear and yell at people, throw food at people, and just stupid stuff. Nothing is wrong with his life at home and when we tried to uncover why the sudden change, he said that I had taken away his best friend and that his best friend wasn't giving him enough attention. So the best friend was trying to pay attention to him and the guy was nice for a while and turned all stupid again. I don't know how to handle the situation or how to approach him about this. We've told him several times to "just stop" but he doesn't know how to grow up. What do I do?

he could be depressed, anger problems, psychological problems...etc

Stop puking rainbows.

Er, talk to him. And, give him a fair shot. Let him know that his best friend is seeing you (His best friend is seeing you right?), and that you guys need time to yourselves. But, if they are actually friends, make sure your guy pays at least some attention. And, if you guys are going to make comitments to hang with this guy, make sure you follow through. It seems that he may be feeling unwanted and or betrayed by his best friend (And for the worst reasons: A girl). Give him the time of day if you really care. If you don't, let him know, and don't let your guy friend lead his friend on.

But, honesty is always the best medicine. So, keep it straight.

Good luck.

Oh, and it might help if you wouldn't call him stupid. Ever think that that may be one of the reasons his is lashing out in the first place? How much more betrayed can you feel? You best friend keeps ditching you for a girl, and to add insult to injury: The girl won't stop making fun of you and calling you stupid.

If you want this solved, you'll know what to do. Otherwise, the kid might just be a jackass. In which case, lose him?

immature guy.he has some problems on controlling his emotion?
you should tell him that we guys would hate you if you continue doing such stupid things.we do care for you but you dont notice that.those kind of things

He needs to learn to control his feelings. Maybe his best friend should give him more attention or you guys should tell him to stop or no one will like him.

People are who they hang out with and if the person is jealous of the people he hangs out with or some conflict happened and no one actually took a effort into solving it then well someones going to be mad. You need to clear up the problem instead of just ignoringing him and just calling him stupid and stuff.
Once you clear out the problem he go on his merry little way.

He sounds immature... tell him how it is:

-Its not your fualt your boyfriend hangs out with you more than him

-personnaly he should grow up and realize that being single in highschool is accually the more mature thing to do...

-he doesn't own his best friend...

either that, or:

-let him flip out and cry until he realizes that it can't be the way he wants... :)

I think his jealously is what lead to his immaturity, which brought out the stubborn side of him to annoy the hell out of people just for some attention, in hope to gain his friendships back.

Whoops, run on sentence, but it sounds educational enough for you to understand what I meant =]

i hope that nobody kills me for saying this... but is there maybe the slightest possibility that he might be gay? i mean he gets jealous as hell because his guy friend is hanging with you .. i mean isnt that going way to far? i mean its not like his friend will never get a girlfriend in his life an jus spend all the time in the world with him i mean he was to fall for some gurl at some point of his life. its just an idea because i never heard of a guy being so jealous that his best friend is hanging out with a gurl that he might like...
but key things you need to do if you want him to stop being immature is first get him, his best friend, and you together and talk about whats going up and what ALL OF YOU GUYS can do together to solve the problem.
2nd suggestion is dont insult him. thats jus not cool. hes going thro possibly a hard time and his additude and aggression might be a call for help.
3rd find a way that all of you guys can hang out so he doesnt feel left out. it doesnt have to be all the time, but jus so he doesnt think that he is losing his friend.

GOOD LUCK!