This doesn't apply to all guys so please don't take offense but I've noticed some guys are just the starey type and try to stare at certain people wih a look so intense they look they want to eat you or something. Or they'll stare like crazy trying to make and maintain eye contact. They just let girls catch them and are blatantly obvious... Why do guys do all this?
I think for some guys it's a way of letting you know they think you're very attractive to them without having the confidence to actually approach and talk to you. I know that having a guy star at you like that can come across rather creepy, but it could just be that they really fancy you, but are too scared and shy to make the approach. Of course some guys may be staring at you simply because they really are creepy! lol