Why is it that guys stare at me from there trucks?

Ok so today me and my mom were driving uptown. I just sit in my seat. LOL. But then i noticed that guys when they ped us would just stare. I saw like five guys do that. I hate it. It always happens to me. I dont like being stared at god dammit. Im a shy person and when guys do it it makes me self concious. I dont even like going into the store because of it. But what does it mean exactly? Im definately not hot. Im not pretty just average. Or maybe im ugly because the guys just stare like there amazed by my ugliness. I really just want to know what it means?