I'm guessing you're in a relatively young age group (guessing grade 7,8 or 9 in school) Because you don't get thiose kind of jerks past that age, well mostly.

What's my opinion, as a friend I'd say to that guy the next time he tries something 'look I've had enough, either put up or shut up.' Thuis is your warning. If he doesn't listen and gets too close (like reaching or pointing or anythign with contact) Then smack him in the nose with your fist (only if he's in a close reange).

As a magician I'd recommend you just stop performing for now. Sit down and practise your heart out, get good with coin or card handling, very very good. If he knows all your stuff then you better practise it much more to hide it better and learn loads more stuf and WELL (so he can't figure them out aswell) When you're ready (give it months) start performing again but don't go over to him and try to show off, still avoid him. But if he does show up again then at least you know your stuff better.

As a man of vendetta I'd start screwing up his magic whenever he performs. And if he doesn't then there you go, next time he jumps in just say 'Why don't you bring your toys in tomorrow and show us all then!'
That'll shut him up. If he does follow these instructions then get ready to switch places and become the jerk yourself

With the words from the great philosipher xyzzy314 " ATTACK HIM!"

Word cuz!

Take a card and slash it across his face hopefully giving him a rather nasty paper cut

Not a good idea. I tried that but the card stuck to his skin and he went to the hospital to get stitches. They won't let me perform for them again, i wonder why

lol muhaha, xyzzy314 lol your crazy man your crazy

just say "hello! your mother is dead, go kiss her corpse"

he'll flip and people will laugh! doesnt matter if he gets angry..
the crowd will definitely support

xyyz did that really happen?

Actually no, but I did end up injuring someone really bad with a deck of cards. Had to run away.

lol get a TT and some stage blood you know what to do then

Combine all of these ideas....

When he comes, finish up the trick you're on and go into a "fake" one, maybe: Have 2 cards selected and meticulously place one to your right and one to your left (both face down). Back up a little and announce that without touching the cards, you will switch them. Pretend to palm the top card of the deck. If he falls for the trap, show your hand empty and say you won't continue with him here. Stop your amazing trick (basically do anything that would seem completely impossible) right there and walk away. This disappoints the kids even more because they thought they were about to see a real miracle, and they'll get even madder at the kid.
If he doesn't fall for the bait for some reason, pretend to just notice him and walk away. It should still work.

TT ok...stage blood I don't need.

dude eveyone needs stage blood when i my break is over im going to have so much fun

With me and spectators it's usually the real thing.

Buy scotch and soda, and slip the centavo in his pocket so when he asks what's in your hand after or while you are doing the trick ask him what is in his pocket.