I shrugged off my share of bullies in my middle- and high school years, mainly kids threatening to kill me with fists for being gay. (Pointing out that I was not, in fact, into boys always struck me as a craven and irrelevant defense, and I don’t suppose anyone would have believed me had I made it.)
But I always felt the biggest bullies, the ones with the most to prove, and the most to gain by exercising their social power over others, were the ones standing at the front of the classrooms. This is not to say, of course, that I didn’t have wonderful teachers; I had several, and I owe them a great debt, forever. But I also had a lot of little emperors, people who seemed to have a lot personally invested in their authority to deny you the right to pee.
I used to wonder what had made their lives so miserable that they took such satisfaction in ruling over a bunch of kids. I still wonder that, actually.