Why do people judge looks so harshly?

Its okay to judge looks,but not in a cruel mean way(No one can really help what they are born looking like). This girl in my cl was looking around the cl saying rude things like, He okay, he aight, uh..he just ugly.Im like,***** you aint a 10 ya damm self.Why do girls do that all the time,i cant stand the ones who are like that.They get on my mother F'N nerves