If he's sweet to you, if he smiles, if he tells you.
I don't know. That is a tough question.
iam in love with this guy but i do not know if he likes me or some other girl
If a guy likes you but you don't know him he may look at you or walk by you whenever possible.
when he says he likes you.
http://www.wikihow.com/Know-if-a-Guy-Likes-You
Not sure how you expect someone to magically know something.
It is ok to like a guy after you know he likes you. That is perfectly normal and a part of life.
You ask the guy.
don't
When he has a penis.
his eyes will open wider if he likes it
Maybe he wants to seem like the tough to get guy in school? If he does like you then, well, ask him.