how should I tell this guy I don't like that I don't like him?

Well, it depends. Have you been going out with him? Or is he just hanging around hoping you'll notice him?

I always believe that you NEVER burn your bridges -- today's geek is tomorrow's millionaire, etc., etc., and people grow in different directions. There's no percentage in telling someone that you DON'T like them. Why be hurtful? If you have been going out with him, just say that you don't think that the relationship is going to be going any further, that you really enjoy just being friends. If he hasn't even asked you out, yet -- why be cruel? Just say "No, but thanks so much for asking me." (It takes a lot of courage for a guy to ask a girl out -- just look at all the posts here in Answers wondering, "Do they like me?" etc., etc.)

Tell them that you'd love to be friends with them because you care about them, but you just can't be in a relationship with them because you fear you might ruin a great friendship.

Just be honest, but fair.. do not rip into the guy, but let him know that you do not care for him and that you wish to cut the ties

say i'm sorry i think of you as more of a friend. i hope this doesn't ruin our friendship. or something like that

just tell him u have a boyfriend

YES. Please make that clear... dont say it in a rude way.. but definitely tell him.