The best prank I ever pulled was on a student. This particular young man -I'll call him "Mike" - was always a pain in the neck in class, forever coming up with little ways to annoy everyone. He would hide things, rearrange stuff on my desk, make obnoxious noises, question every little thing just to waste time, and so on. Finally I told him that I had thought of a way to get even with him, and that I was going to do it on April Fool's day. For weeks I gave him the countdown; every time I saw him, it would be "Hey, Mike, only x days left until April Fool's day!"
The joke was that I didn't have anything planned for April Fool's day. It was all about the suspense. And it worked, too...Mike cut school on April Fool's day, telling his friends he was so afraid of what I had planned for revenge that he didn't dare show up.