A class of 15 year olds were waiting for French. The teacher had a reputation for a certain gayness; hand gestures, vocal lilt, being a French teacher - all conspired to colour him gay.
Gays being fundamentally unreliable, he was late for one lesson, presumably having been distracted by the new handbag shop in town. Five minutes into the lesson he burts through the door, huffing and especially puffing, and pants "Sorry, lads. Cock up my end."

"But I SUCK at oral!" complained Alexandra Cooper, the day before the oral portion of our German test. Mr. Keenan decided to commiserate with her while using her own slang to make her feel more at ease. Or something.

"Yes, I've always, uh, 'sucked' at oral too, but..."

The rest of his sentence was drowned out as the inevitable hilarity ensued.

After a lengthy motivational cum bollocking lecture, our American maths teacher told us, in all earnesty, "Yeah, I know I ride you guys pretty hard sometimes."

A couple of the Set 1 GCSE Maths class popped over to our Set 2 class one day, in order to tell us that our teacher, an awkward, sartorially challenged man, was "a bender".
They did this with black marker pen in capitals on every one of a stack of about forty textbooks, and then legged it and left us to suffer. Cue the head of maths, possibly from the Middle East somewhere, shouting in his Borat-esque accent that "That man has had more women than all of you have had hot dinners!" I didn't know where to put my face.