Kids Can Be So Cruel

That's the thing people always say. Parents take the cruelty of other kids into account when they name their babies. Kids say things to each other that your boss would get fired for saying. Kids do things to each other that, if adults did them, they'd be arrested and charged with assault. 
Why do we say it with such resignation? We can all agree it's bad, but we all accept it's inevitable. 
I'm curious if this is universal across cultures. I wonder if there's something more that can be done about it besides some YouTube videos and an occasional school assembly. 
But you know what? I remember this once in grade schools I flipped the hell out on some kids who were picking on me. I just snapped. I can't remember which bullies or what they were doing that resulted in my flipping, but you know, occasionally other kids spit in my hair. Made games of bull-rushing me and knocking me down as soon as the recess lady was otherwise occupied. 
Someone took me (and not the bullies, by the way) to the office and sat me down with the principal. I can still remember how I was sobbing so hard I couldn't breathe. My hands were shaking so hard I couldn't wipe my nose with the Kleenex the secretary gave me.
The principal honestly thought she was being helpful when she sat me down and explained to me how I needed to grow a thicker skin. How my life would be much easier if I wasn't always trying to be different (as if this was something I had a say in). She told me it was okay to lie a little and pretend to like the bands the other kids did. The other kids wouldn't change, she said, so if I wanted them to leave me alone, I would have to.
This isn't a sob story so much as a hopeful one. They've finally started caring about bullying, stopped being so resigned to its existence. If that woman is still a principal, I highly doubt she's as tone deaf as she was then. And I suspect it's more common for the bullies to get the talkings-to. 
Know what's funny? I know all that bullying made me stronger. Made me more empathetic; made me care less about what other people think.