Here’s another one I did as a teacher.
There was one kid who couldn’t keep his mouth shut during tests (OK, maybe more than one- but one who was really loud) and I decided to use it against him.
For one question on a trigonometry test I had a picture of a triangle and under the base it said “x = 27” but on his test I put in a different page that said “x = ?”. The question was to “solve for ‘x'”.
Sure enough one guy raises his hand and says “Mr. Pepper, I think you made a mistake on number 7”. Looking down at my copy I said, “Whoops, I think I just gave everyone a freebie”. The class started chuckling except for this guy who said “there’s no way to do it”. Now the class was laughing. He just kept on going at how there was no solution.
After the test, when he figured out what happened he told me I was going to regret it.
Knowing him I probably did.