When I was a child I thought that bullying in schools could only happen amongst the students. It never occurred to me that the biggest bullies of all are none other than the school principals thermselves.

http://diary-of-a-school-teacher.blogspot.com

Some teachers have their ego trip.

...these are the decadence of politics that happen almost anywhere. It'll be only too obvious that you will feel that you are alone in this world, knwoing everyone else is agaisnt you, calling you names, and accuse you of being idealistic, until of course, until you met people who share the same ideals as you.

You're not alone about this. Let's just say there was a system that is actually running the society so perfectly that it will warrant anyone to be as malicious as you've stated about the principal and the backstabbing teachers. It is a form of decadence, and the bad news is:

Only a few are aware of it, and many of them rather succumb to it.

This so called "big fish eat small fish"

so principal is just like every other normal boss. they just being bullish.

Maybe the teacher use nagging/bully student to release their inner anger especially when it related to their personal/family problems.

Err.. what's that got to do with the topic?
Well, principals are human too.. When they feel inferior or threatened, they will do their best to keep their positions. That includes backstabbing etc..

The school is a playground and everyone is a sandbag. The only difference is who boxes which.