How do i tell this kid to go fly a kite?

I can't stand him. He is cool to go to the mall or a party with. Basically if there is girls around i can hang out with him. But I can't stand him when we are alone. He is always talking about how he is in a gang and blah blah blah. But he's a little punk and i know it. But its like any group of people i hangout with he shows up there. Like he started coming into the weight room and hanging out with me and the football team. Then yesterday i was having lunch at white cat (asian place) and he just comes in and sits with me and a totally different group of friends. He doesn't know them at all. Then today i stopped by my school to meet some friends and he is with one of them. They don't like him but they let him hang around because they can sell him weed for stupid prices. He doesn't even smoke he just buys it to look cool i guess. I wanna tell this kid to go away but i don't want to be rude about it. I don't go to his school anymore so i thought that i wasn't gonna see him much. But he is always around.