I dont like him! what should i do?

so there is this really annoying kid that sits in front of me in homeroom.although he is extremely annoying, he is a nice guy. but i dont like him....at all. he is pretty nerdy (and really short) my friend told me he is going to ask me out sometime this week and i dont know what to say to him that will give him the clue that i dont like him but still be nice. he has tried to ask me out before, but before he got to it i freaked out and told him i was grounded so he left me alone for a while. the kid just wont give up...help meee!!!