Why are women mean to each other?

I'm genuinely curious. Is this a result of the patriarchy making women compete with each other for men?

Most women know what I mean especially if you're attractive and dress good women tend to be meaner to you. It's as if you were a threat to them.

Any girls who experienced this or men who have witnessed this?

Why are they so mean to each other. The whole girls girls thing is a hoax. SO many women are constantly competing and want to be better than the next women. Whats going on?, its so rare to find women who are kind to other women.