There was this quiet lass in our school, Sabrina, she was nice and hippy-ish. Didn't talk much, but when she did she was very pleasant and articulate. Used to just do her own thing, going around sketching stuff during lunch breaks, was obviously destined for art college, etc etc.
One day in 5th year maths [so about 15-16] the teacher asked her a question. It was a drowsy summer day, last period, she was staring out the window at a bird. Sabrina goes "Oh sorry, I didn't hear you", teacher makes a weak joke about "Staring at a bird, eh? Well, I won't call you a bird-brain..." and Sabrina fucking flips. Shoots to her feet, starts screaming at the top of her lungs, launches her chair at the teacher, and proceeds to sprint up the classroom and deck the teacher with a Tyson-esque left hook. We all sat in stunned silence, Sabrina rips the whiteboard off the wall and hurls it, lays a couple of kicks into the prone Mrs. McLeod, then starts smashing the shit on the teacher's desk. Another maths teacher, hearing the commotion, comes in and immediately tells us all to leave, realises Sabrina's not to be reasoned with, and basically drags Mrs. McLeod out and locks Sabrina in. We could hear her in there, shrieking and swearing and smashing, and the next day when we went to check the room/retrieve our bags the room was totalled. Windows broken, ceiling tiles all smashed out, lights all broken, a huge percentage of the furniture absolutely wrecked. Even those heavy duty tables, that're designed to be abused by pupils all day every day, she'd broken a couple.
The police arrived pronto, and we watched four burly policeman struggling to lift out a struggling Sabrina. They'd cuffed her hands AND feet, but she was still thrashing and shrieking, and giving these big lads a legitimate hard time. Eventually they got her into the van, and Sabrina never our school again.
Now, the thing that made it weird and the school's Big Drama for a while was this: We all saw Sabrina a couple of weeks later, now a student at the next door Catholic school, and she was totally the same as usual. Pleasant, friendly, artsy, kinda quiet. When asked about her annihilating room B21, she just kinda smiled and said "Oh don't worry about it". And the topic was absolutely forbidden at our school. The teachers were totally closed doors, Omerta kinda stuff, and asking any of them at any time about the Sabrina Incident would get you instant detention, 0 warning, 0 exceptions. Even your normally more lenient teachers, like Mr. Conlon who would smoke weed and play Grand Theft Auto over LAN with us during lunchtimes, were absolutely zero tolerance on it. Was weird.
I've seen Sabrina around since then, and she's now a hippy yummy mummy, still goes around sketching stuff, occasionally see her selling [absolutely amazing] paintings at art markets and stuff. I'm always tempted to ask her what happened, but I always had a bit of a blind spot for a left hook, so best not to bother.