*Rubs hands together* Okay, I'm a Women's Studies minor, and we have tried to take a crack at this for ages. I agree with what everyone has said--especially about narcissism! Narcissistic personalities have such fragile egos that they MUST focus on themselves to constantly reassure their insecurities. They have no energy for anyone else, as that someone else could reject them, thus blowing their ego to pieces.
The interesting bit of female behavior comes into play as the "dominant" or "alpha" female feels threatened. Notice that if the woman doesn't feel threatened, she has no reason to strike out, and really doesn't. If, for example, you are new to a school and find yourself the victim of a popular (or even not so popular) girl's insults, it's her (hurtful) way of exerting her dominance over the domain. By putting you down, she is trying to ensure that you do not become a threat and steal her position.
The same goes outside of school, in work, dating, and social situations. When a woman feels threatened (or IS threatened) she strikes out. But whereas men strike out really directly (e.g. WTF MAN, YOU'S A DOUCHE GET AWAY D:<) women are much more skilled with the complexities of indirect communication. While these skills provide women with excellent intuition, they are also the weapons with which we hurt each other. The intuition that lets us know a friend is feeling down and tells us to help her out, also tells us that there's a girl rising on our scene and we need to hit her vulnerable spots.
Notice that women only get into physical fights when things REALLY escalate, and even then they vastly prefer verbal and indirect non-physical communication. As women we have less testosterone, therefore less aggression. But we have the same feelings of being threatened or insecure as men do. We don't have the urge to punch our rival in the face (...usually...) but instead to spread nasty rumors and backstab. Women are smart, skilled, and dangerous. When they feel threatened...well, we like to show off how very sharp our tools are!
Sorry, that was long.