EDIT: Alright here's what you do:
He's a senior, you're a sophomore.. He believes he can do whatever he wants and get away with it. Next time he does it, stand up and say "Alright, shut the hell up. Yeah, I play RuneScape on occasion, it's just another video game." If he persists, tell him "Look, I don't know what's worse. The fact that I play RuneScape or the fact that you get off to trying to be the big guy and making fun of me for it. Shut the fuck up and stay out of my business." Then go along with your day. If he says anything about you being butthurt or anything, don't worry about it. You just made him look like an ass in front of everyone. Surprise him, stand up for yourself. He feeds off of bullying you and the moment you say something he'll get into defensive mode and start talking out of his ass. If he says anything about fighting, tell him "You make fun of me for playing a video game. Now you want to fight me so you can try and get back on your high horse? Grow up." PUT HIM IN HIS PLACE.