I had one shop teacher (he's a real creep and also doesn't know when to keep his mouth shut) who decided to say out loud, next to a classmate, something about a chemical imbalance in my brain, because I guess I was failing. So I have him this blank stare for about ten seconds, and he was rambling on about it (didn't mean to but I spaced out at that point) so I put in my noise reducing headphones and walked away to the other side of the school.
He followed me to that corner and continued talking to me, while I had my beats over my ears, and wouldn't shut up. So I just fixed my eyes on one spot on the wall, opened my backpack and started eating a sandwich. He must have been convinced I was almost catatonic XD.
Anyways this guy was a creep, asking 7the grade girls for hugs, and since no teachers did anything about him, I basically ended up intimidating him out of his own job. I kinda have a gift for intimidating bad people with few words and actions.
That's the only time I faked dissociation or catatonia.