I already told you, mean girls are a manifestation of a patriarchal dominance hierarchy system, which strictly speaking isn't about men - it's a social system.
A dominance hierarchy (which is what patriarchy actually is, not just a dynamic between men and women) is about maintaining traditional power through displays of aggression, coercion, and artificial barriers to true competition. Police brutality is a symptom of living in this sort of system, as is sexual harassment and violence against gay and trans people. Those are all examples of using violence to dominate others who are seen to be lower down the pecking order.
Our social system revolves around clawing your way to as high in the pecking order as you can get, by any means necessary, including violently holding other people down or erecting barriers to them being able to compete — all the while telling yourself that you’ve earned your place fair and square. This is how a dominance-based hierarchy functions and it dovetails nicely with the rather brutal brand of capitalism that is practiced here in the US. It’s the complete antithesis of a merit-based system, and it requires an underclass to support the base of the pyramid of power and privilege. Without underclasses, there is no apex — a large part of why a flatter playing field feels disruptive. People aspiring to the top of the pyramid understand this, albeit largely subconsciously.
