What's this guy's deal?

He’s the only one who could answer that question I think. Maybe you look like somebody he knows that he doesn’t want to talk to or even see.

@snowberry took my answer, verbatum.
Maybe you resemble his mother, and who wants mommy at school with them?
There’s a multitude of innocent possibilities. I would SO not worry about it.

Why are you asking us to guess when it is so very easy to simply ASK HIM?

I would ask him.

Nothing, ignore him. If he had an actual problem with you, he’d come and tell you, not sulking like a kid. He obviously doesn’t like you for whatever reason, but that’s not any of your business.

You should be worried if he’s following you everywhere not the other way round. May be he wants you to be curious about him which is why acting in that fashion.

Ignore him. He probably thinks you’re someone else.

Maybe he heard some gossip about you from someone you know and has the wrong idea about you?
People lie, maybe he know’s a pissed off ex of yours or something?
If it were me next time I see him around I’d purposely find a reason to veer in his direction like I’m going somewhere and he’s in my way and I’d look up at him right in his eyes and say “Oh, sorry I didn’t see you there, excuse me.”
Then I’d gauge his reaction and see if he replies with a smile and say’s “No problem” or if he scoffs and looks the other way like he’s irritated?
Who knows what people’s problem is sometimes?
I used to work at this school and teacher’s would say hi and try to talk to me as walked down the hall except for this one woman who I’d say hi to and she’d just ignore me and look pissed off.
On the rare occasion she would surprise me and say hi as she walked by.
I heard from people that she suffered from really bad psoriasis (it’s like a skin condition) and she also had a gambling addiction.
So I imagine some days she was really depressed and maybe her reaction when I’d walk by had nothing to do with me at all.
Anyway, people are interesting.
I just try to be nice to everyone because who knows what they might be going through.
Good luck.

Is it possible you’re misinterpreting his actions? Perhaps you make him uncomfortable because you’re always looking at him when you see him. Just don’t look at him any more and see if he relaxes.

He might be wondering why you are always staring at him.

He may think you are someone else.

He may know you from somewhere else, maybe from a long time ago, and maybe you don’t remember him, but he remembers you for some odd reason.

Like some of the others have said, maybe he heard some bad gossip about you, from who knows, which is unfortunate.

Maybe next time you see him, you could stop him and say, “Do I know you from somewhere? You look really familiar.” That way, you’re not exactly calling him out. Then see how he reacts.

I find the best thing to do is never ponder someone’s behavior, it could drive you nuts. I have two neighbors that walk with their heads to the opposite side when I pass. (They live together) else I’d be worried if they lived either side!!

Some people have mental illness, some people just act odd for no reason, some people have an issue, but really it’s not your issue. Focus on your friends and people who are meaningful to you. The one’s that actually talk to you and make you feel good.