1) This is one of the most shallow questions ever, guys have personalities too! Do all girls act the same when they like a guy? No, they don't! But I guess I can forgive that. :)
2) I am a guy, and if I liked someone, I'd probably not say anything at all around them. I'd have too many butterflies in my stomach to say anything.
3) For a lot of other guys, they really just couldn't get enough of you. They would just keep looking at you, maybe lightly abuse you a bit.
Well, you could just ask him, its not like he'll hate you after that, he'll either say yes or no, but if you can't, then usually you can tell cauze he'll pick on you, talk to you alot, but, sometimes they just like you as a friend, so it's hard to tell unless you ask.
If the guy/girl is showing you signs dat are noticable den you'll know right away if the guy/girl is showing you mixed signals wait till he/she comes to you and tells you.. other then dat have fun ! good luck