How come some people are so insecure, mean, and jealous? Does everyone have a tendency 4 negative disposition?

I know what your saying now a days if a girl is skinny and wearing a Minny skirt all of a sudden guys like her even if she isn't beautiful at all. i think lots of people are insecure and mean because they are so insecure and they aren't happy with themselves. but not everybody is like that and it is so true how so many people in Hollywood are all so fake but actually I don't think Charlize thereon is ugly at all she is one of the 5 most pretty girls in Hollywood and so is Marilyn Monroe.