When I was first came to the yeshiva there was an altah bochur who decided one year to set up a “pool” for sefirah, where everybody put in money and whoever finished split the money.
So we figured it was a good way to make sure we finished, so why not. So we all bought in, and then he spent the rest of sfirah sabotaging everyone. He would change the sign in the beis medrash like 5 times a day, and nobody would remember what day it was, and one day he was the chazzan and he davka said the wrong day so that everyone would be tricked, and many more tricks that I don’t want to say in case I ever decide pull them on you.