In the 4th grade I was at a private school. There was this really asshole kid there. He used to pick fights with kids and/or beat them up. His friends would help him out too, they would help by pinning his victim down or helping to corner him. On the rare occasion he lost or was fended off, he would go tell a teacher that his would-be victim had attacked HIM.
I was one of his favorite punching bags. I'd try telling a teacher but I was the one who got in trouble, because according to the kid's parents he had "issues" and it wasn't his fault. Worse still, he would then have his parents tell the school I was lying. That got me sent to the office a few times.
One day on the playground his friends grabbed my arms. He came up to me spouting the usual shit talk. I don't know what changed this time, but instead of being scared, I was just pissed. I kicked backwards and hit the two kids holding me, and they let go. The kid tried to punch me, but I grabbed his arm and threw him to the ground. He started screaming, and went to the teacher. They sent me to the principal's office, and I was shocked that this time he actually heard me out. The kid was a bully and I had defended myself. He sent me back to class and the bully got a detention.
However, the next day I got called back to the office, and the principal had acted like he hadn't just let me off. Apparently he had gotten a letter from the bully's parents saying I had "attacked him and his friends" and that they were defenseless. They were apparently also wealthy contributors to the school, and they threatened to pull their grant if "students who contributed to a negative atmosphere" (they named me, in particular) were allowed to remain. So I was expelled. On the spot.
So basically, some playground bully had his parents bribe the school to expel me.