When I was in college, my life (as well as those of about 30 other cadets) was made miserable by a calculus instructor, who was doubtless brilliant, but a hopeless teacher. An example, he had to grade on a curve so as not to fail the entire class; I once got a C+ on an exam with a 13% score.

We exacted a small bit of vengeance by harmless pranks.

First, we removed every scrap of chalk from the classroom. Giving us a blissful 15 minutes of peace while he acquired more.

Next day, we removed the erasers. It was difficult not to laugh as he filled every scrap of the chalk board with meaningless gibberish, while looking high and low for a menas to remove some of his scribbling.

Third day, every desk in the room was facing the opposite direction. As there were chalk boards on that end of the room as well, he actually had to check the pacard above the door (twice) before satisfying himself he was in the correct room. (No, he didn't recognize any of the members of his class...he had no connection whatsoever to his students.)

The fourth day? No desks at all. We were all sitting on the floor, ready to attentively take notes....

Now, we weren't malicious. We did nothing to harm the man. But we had to find a vent for our frustration at being required to endure this inadequate instructor. We were a motivated bunch. We wanted to learn from him. But his disdain for lesser minds made him incapable of teaching.

So, no regrets on that one.