I am taught that hurting a bully isn't helping anyone. Now, you've taken that bully's place as bully, and nobody wants to do that. But, if you stand by and do nothing--well, it matters your idea of "nothing". If nothing means showing no emotion at all when they insult you or destroy your work, then that might work in the long-run. If nothing means showing that you are in distress and crying about it, the bully will probably be saying to his buddies, "Woo! I made that nerd cry! Look at me! Haha!"
But, how I would go about it is to pretend that you are friends with the guy, and you act in a friendly way towards him. Example:
Bully: You're so dumb!
Girl: Well, 'dumb' seems a bit severe. How about you use 'lacking of information' instead? It would make people feel a lot better.
Bully: I don't care what you think, idiot!
Girl: Oh, okay. Well, then, I'm afraid there is no point to this conversation.
Bully: *doesn't know what to say* Get on your way, dork.
Girl: Bye. Oh, and try to use a bit kinder vocabulary! I think you and the person you're directing it to will feel better. c:
You don't have to act cocky or sassy, just kind, with plenty of smiles. No bully really feels good about hurting other people, they just feel good that people "respect" and fear them, and they are on top. Just show them that you aren't a threat to them, nor are you vulnerable to their reign. Show them you are your own person, your own self, your own "pack". You are the alpha of that pack. They don't rule you, and you don't rule them.
"Don't show them who's boss, show them who's friend." ~Twizzy