A few times for me. Once while walking in line in 8th grade, some kid was horsing around with another kid and I got kicked by one of them, so I got pissed off and kicked the kid who kicked me, but I was the one who the assistant principal saw and he viewed me as the aggressor, so he kicked me right in my ass! I lost it and went to punch him but missed, so I took out my pen and threw it at him and it stuck in his neck momentarily before falling out. A lucky shot to say the least. I walked out of the school and went home to tell my parents and the matter was handled when my folks called the police, and there were witnesses on both sides so no charges came against me or the assistant principal, but he never messed with me again. I ended up beating the shit out of the kid who started it all a few days later.
One other time, on my very first day as a freshman in high school, I was just sitting at my desk in my home room, first class of the day, when 1 guy came and put me in a choke hold from behind, being a student of the martial arts at the time I grabbed his hand and bent his finger to make him let go, after making him back off, I punched him in the nose causing a lot of blood to gush out, then another kid, a friend of his, came at me, so I picked up my desk and deposited it on top of his head. I was subsequently expelled for a week, and resumed my classes without being hassled ever again. In case your wondering, I grew up in Chicago's NW side, and attended Senn high school. Other then times when people tried to bully me, I was a good kid.