Search Results: she acts strange sometimes

I've meet this guy few months ago. He is loud, confident guy that usually stands out in group.

His guys are always normal, around me when he's not with them. They talk to me. When he's with them they start to ignore me and act pretty strange.

This guys acted few times normal and it was surprise for me but usually he doesn't talk to me, sometimes i catch him looking at me, treat me different. They sometimes have they own "jokes" about me and i don't know why.
It all started in our first interaction when i borrowed him something and he looked at friend and that friend said my name loud and smiled at him.

Once i was texting and he like brushed next to me and stopped for second and than acted like nothing happened (i was next to my table and there was planty of space). When I catch him looking he looks away or run through his hair with hand and looks away.

He looks at me when he's passing, sometimes he didn't noticed me.
But also when i was coming they looked t me and when i came closer they turned like they didn't see me even they know i saw them looking.

There's more stuff when he acted pretty weird but i don't know why. He has girlfriend and they seem pretty happy together.
What is deal with him?
If there is another explanation please write it down! :)

So guys why would you do that?

If guy only acts strange torwards one girl, when she catch him looking he looks away or runs with hand trough hair and look away. Looks at her from far but when he's close to her he ignores her. Sometimes comment her and treat her different in that strange (childish) way.

This guy from my class acts strange only torwards me. He's CONFIDENT guy and loud and always stands out in class.
He has a girlfriend i thing for 1-2 years.

Also he's been pretty strange torwards me. Him and his one guy friend sometimes comment something about me or have their thing and it all started with my and his first interaction. Since than it was weird.
He's sometimes pretty normal torwards me but usually it's like he ignores me but looks at me. I catch him staring often and he looks away or he run his hand through his hair and looks away.
Few times he started to act normal torwards me but it lasted short.
He always talk to my friend normal when i'm with her and ignores me but usually she hates him.

I taught first that he hates me but he sometimes acts nice and his guys are normal torwards me but he still like he avoids me. They started to going out to smoke where me and my friend go.

Why? Why he's hot and cold? He stares and i catch him and when he's passing me he act like i don't exist?