How to get rid of someone?

There's this kid who says I'm his "Best-est best friend". I keep telling him we are not friends but he's in denial. I'm moving to a new school from my old private one (I only went for a year) but, against all odds, HE'S GOING TO BE THERE. I want to start fresh, but I'm pretty sure, if I keep saying no, he'll tell all the bad stuff about me. I'm just a teenage boy who wants to have fun, but if he doesn't go away, that's not going to happen. If you think I should be his friend, think again. His cr*ps his pants (Sister told everyone, and he didn't deny it), he smells awful, he farts to make everyone mad. I'm a boy and boys can be disgusting but this kid is abusing the right. My friend, who is staying at my old school, says I'll miss you, but she won't miss the guy who's bothering me. I can just tell him "I hate you, get out of my life." But he's just gonna move is big, red, annoying mouth, and babble to me and everyone. How can I teach him a lesson? Also, my old best friend is going to be at my new school, so please. I gave him a chance but he is just, a maniac. He had to pay people to hang with him. Help me :(