How do I deal with this "bully"?

There's this guy at my school who seems to have something against me.

Why?
I don't know...

I met this guy like twice before and when I did, it was when I was in the locker room at my school.
The two times, I had to go somewhere, it was really crowded and he was in the way.

I just said "watch out" politely and he started saying something like "What? You trying to start something fool? Don't tell me to watch out ******. I'll beat your ***".
I said "...um no I need to go somewhere. Sorry."

Then just today I guess he was behind me in the hallway and lightly smacked me in the back of the head. I turned around and saw him laughing. Then he just shoved me out the way.

I didn't say anything as the principle was near us, but I really don't like fighting anyways.

What is this guy's problem and what should I do about him?

Are you in middle/high school? At that age a lot of guys bully other guys because of their own insecurities. The guy is probably incredibly insecure and bullies others to make himself look more tough/cool, and also to make himself feel better. On the inside, he's probably pretty down, though.

When people are mean to me I always ignore them completely or laugh it off to make it seem like I don't care. He's just looking for you to get upset, and if you don't get upset like he wants, he should eventually stop and move on. And by "laugh it off" I mean make it seem like you really don't care. When he tells you "What do you mean watch out?" etc. I would just be like "Haha I'm walking behind you. Didn't wanna hit you" in a casual way.....I don't know. Just don't let him get to you.

If it gets really bad, tell someone. Seriously.

That person that's bugging you is probably just insecure so don't let it bother. There will always be bullies in life trust me, but just ignore him or ask him what his problem is (politely). People bully others for various reasons, but at least you know you have something he's missing from his life :)

You should've reported him to the principal right then and there. Don't say anything or try to fight him. Just handle it with the principal and tell him or her what's goin on. You don't wan't to get expelled!! What would that solve? Good luck!

well if u dnt lik fighting follow a teacher or princibles time buget then try to get him to hit u wen there around and ur probs solved and if that doesnt work get some one older thats ur mate and tell him or sumfin if that doesnt wrk i dnt no sorry

stick up to em like me I'm ten guys push me around i sack them and then get in to a technical fight and then once they lose they will get laughed at for the life :)

If really was and accident and this student doesn't realize it even that you offered apologizes then you need to report him to the office principal or the school authorities and say exactly what happened,make sure to do a writen report with all the details don't escape a single one, make several copies in that way you will have a verval and a writen report.
Also tell your parents if they don't listen you can do a police report too and say that you don't feel safe around someone who insult, assault, and bully you and disturb you time in school that at the same time you can't study because this student is abusing you piscologically. Be firm and don't hesitate in you statements, make noise other wise this idiot will keep going giving you hard time.
Let him know in a very polite and firm voice in front your teacher that you don't appreciate his behavior and he need to stop.
Remain him that he need to keep his violence in his house.
Besides go to a violence domestic group and report him because this type of pseudo students only create problems no matter in what place they are. and we need to get rid of them.
so go ahead and don't be afraid to speak.

He is a bully and you caught his attention for some reason. Either he thinks you are an easy target for his amusement (really others). He maybe thinks he is the big man on campus and wants other people to believe it too. He wants attention so don't give it to him. Pretend he doesn't exist. Ignore him. If you can't then tell him to please get a life, stop messing with yours.

edit: Or you could embarrass me (tread carefully here) by saying, yo dude, stop. It's embarrassing. I'm not gay.

This could be a dangerous thing so....