I notice this guy staring at me for many times in class, I thought he like me at first but then I found out he has a GF, and he knows I have a Boyfriend too, but he just keep looking at me, wandering around where I am but doesn't talk to me anymore, I don't understand why he is doing this but it just make me annoyed. Is it rude if I say to him to stop looking at me?. He is used to be nice to me before but not anymore and I don't know the reason.
If you say something like "Hey, will you please stop looking at me!?" the guy would just shrugged his shoulder and say "I ain't looking at you! What makes you think I'm looking at you?" and you'll just end up looking like an idiot.
Just don't mind him. People who stares long at people are usually interested. But who else don't get interested with random stuffs around us?
Don't appear conscious or uncomfortable. It will make him look/stare at you more.