The “popular mean girls” being rude to you isn’t a matter of being “unpopular”, they’re just rude to everyone not in their friend group. (Not sure if this is unpopular)

Girls, especially teenage girls, have a sort of social hierarchy. A lot of teenage girl life is basically trying to figure out where they fit into this hierarchy and it drives a lot of the relationship dynamics between girls. Not every girl necessarily wants to be the "queen bee" either. In this context, some of the things girls do start to make a little more sense.