Gender Roles

Girls wear pink, boys were blue. Girls wear dresses, boys wear pants. Girls play with dolls, boys play with trucks. Girls cheer and dance, boys play and get dirty. But when did it begin that a gender role for girls to act like completely horrible to one another. Girls are so mean to eachother that they even felt that it was appropriate to make a movie out of it for humor. I know every girl has experienced it, even if they were the ones at one point were the girls that I am talking about. I have had conversations with friends that you know how good you look on a Friday night not by how many guys come and talk to you but my how many dirty looks you get from the other girls that are at the same establishment. Does anyone agree with me? Why is it like this? Do you think boys have to deal with the same thing that girls do?