Inspired by this, I created a piece of April Fool's Day prank software for my dad...
Our computer runs pretty slow normally, and he is always getting irritated by it. So, I wrote a VB program that runs at startup (in his account only) and displays a message stating that the computer is tired of his impatience and is going on strike, and will load when he is more patient. When he closes the box, he is force logged off

... He'll get a kick out of it, but I just have to disable it before my mom gets on or it could be bad... Or she might get a kick out of it too, even though it's not aimed at her...
I can zip it up and post it here if someone wants it

.