What does it mean when a guy calls you uglybut stares at you a lot?

I assume this guy is more a boy than a man; boys will often tease or insult girls to whom they are sexually or romantically attracted. It is a sign of immaturity and should wane as the boy ages. If you observe this behavior in a man, then he is extremely immature or has other problems and you might best avoid him. (You might best avoid a boy who exhibits this behavior, too, and wait until he grows up a bit.)