What do you say to a guy when he knows he likes you and you like him?

Well do you? If you don't you steer clear. If you do you show more affection.

That depends on if you really do like him and if he likes you.

If you really do like him (he's right), and you think he likes you too: tell him. It'll feel go to get it off your chest and then the two of you can try dating each other. If you like him then you'd want to date him.

If you don't like him (he's wrong), but you think he likes you: Politely tell him that you aren't interested in him like that, sorry, but that your interested in being friends (unless you don't want to be friends with him, then just leave that part out)

If you do like him (he's right), but you think he doesn't like you: See this is the hard one. Do you tell him it's true when you think he'll say he doesn't feel the same way? Or do you tell him it's not true? I say talk to him; find out why he thinks you like him. Then decide based on what you feel is right. It all depends on the situation.

If you don't like him (he's wrong), and you don't think he like you either: Just tell him no politely, and that you only think of him as a friend (unless your not friends with him. Then just leave that part out).

If you don't really know if you like him or not: Be honest. Tell him you don't really know what your feelings towards him are, and that your trying to figure it out. That way, if he wants you to like him, he has some hope. And if he doesn't like you back, he will just wonder what you'll decide.

Either way, don't avoid him. He'll think your mad at him or something (trust me, this happened to a friend of mine). Decide what your going to tell him really quickly so that he doesn't bring it up when your unprepared.