Slaughter High

The rotten, popular kids punk high-school geek Marty (Simon Scuddamore, who, as far as anyone knows, never worked in movies before or since), when Carol (Caroline Munro) gets him into a shower in the girls' locker room, and makes him think she's going to do the nasty with him. It's all a set-up, with video cameras and Marty's privates exposed for everyone to see, and Marty's head getting jammed down a toilet (and, in some ways, it's all rather reminiscent of the opening scene of Carrie)...
But the mean kids don't stop there: They give Marty a joint, and in a chemistry-lab mishap involving nitric acid, he catches fire. But, of course, Marty isn't dead — just really badly scarred — and, as far as the mean kids know, he's been committed to a hospital somewhere.