Isn't it great to develop crushes on complete strangers. The fact that you never get to know them and don't have real expectations makes it so easy and much more fun than people you actually have to talk to. You just give him a nickname like Smashing Pumpkins Kid, Green Suede Shoes, or The Math TA and imagine what a wonderful and amazing person he must be. You look away when he notices you looking and don't really give him a thought outside of the time spent in class or at Bert's. It's like a celebrity crush, but better because he's real.