Very good one! I remember back when Windows 3.1 came out and I was still learning Windows someone gave a program to me and said if I install it on my computer I'll have some cool screensavers and games to play. Well, gullable as I was I installed it and all of a sudden an error message popped up saying the program cause a general failure only had an OK button. So, I clicked OK and another error came up and only OK to click and it happened one after the other until my whole screen became distorted and eventually black. I thought I had lost my computer until another message came up saying: "HAHAHA!!! I bet you had a good fright!!! Relax it's a joke!". Needless to say I was to relieved to be cross! I still want to pull a prank like that on someone!