guys you like that don't like you

Well, since I don't know what gender is attachable to memera, I'll answer this question twice.

(memera is female)
Could be the guy's simply not interested in you. Maybe he doesn't think you're attractive. Maybe you're not his type. Maybe he's in a relationship (that you don't know about?). Maybe he's shy too. Maybe he's gay.

The only real way you're going to find out is if you talk to him. Just cowboy up and say something. You might not want to come right out with a feelings talk, but you can certainly introduce yourself or spark up a conversation about something. Witty remarks are great, but don't plan for your entire interaction to be clever improv. If you're this nervous about the person and don't plan a little bit, you'll probably clam up.

I suggest thinking of two or three things to talk about and be ready to go wherever it goes. After that, you're good. Just drop hints if you're comfortable with it and wait for him to make a move. Or... if you're more adventurous than that, wait an appropriate amount of time and make a move yourself.

(memera is male)
Could be the guy's simply not interested in you. Maybe he doesn't think you're attractive. Maybe you're not his type. Maybe he's in a relationship (that you don't know about?). Maybe he's shy too. Maybe he's straight.

I suppose my suggestion here is pretty similar to the former with a couple of exceptions. First, make for damn sure that he's gay. Otherwise, there's going to be some real awkwardness and embarrassment for one or both of you in the near future.

Other than that, it's basically the same. Man up, say something, and be appropriate.

And finally... which is it?