I don't agree Sofs.
I agree in principal that men and women are likely to bully equally as much, but I don't agree that it is a bully's negative perception of his or herself that drives them to bully.
There could be a myriad of reasons why someone bullies others. They could be being bullied or abused at home or they could have stumbled upon a method of getting their own way to name just two.
Negative self-perception is not one that I would put at the top of the list though.