Ok, now this is diabolic:
When he was a prof at Stanford Carl Djarassi (the. director of the research that led to birth control pills) asked all of his students to come up with the most difficult question they could think of for their up-coming final exam. He said it was for purposes of making out the test. Of course, each student put together a question that he thought other students couldn't answer; that way their grade would be better since everybody would be in the same boat. On the day of the final Djarrasi handed each student their final exam. It was the question they had put together earlier.
I was tempted to do this myself a couple of times, but was just too damn sneaky.