Our teacher hadn't turned up, so we were making a steadily increasing amount of noise. We eventually attracted the attention of Mr. Cowley, who asked me to report that a supply teacher was required.
I refused a couple of times, showing off, until Cowley became irritated, and threatened me with detention. So I slouched off, grumbling, to find the year head. As I walked past Cowley, and in full view of the class, he smacked my arse.
I was fifteen at the time and horrified for 2 similar, but distinct reasons:

1. Bender Cowley had just smacked my arse.
2. Bender Cowley had just smacked my arse in front of all my mates.

He may well have meant it as a gesture to snap me out of my slouch and speed me up, but to everyone in the class, it was a private, tender moment of bum-fondling between two very gay lovers.
They proceeded to draw cartoons of Cowley doing various foul things to me, culminating in a cartoon on the main notice board, of me being fisted by Cowley whilst wearing a bondage mask and a speech bubble protruding from my mouth declaring that I didn't want him to use any lubricant.