I got banned for posting shockmeme site sourmath.com at GAF
I did warn them what it did though.
What it does (advisable to read this before visiting the site):
spoiler (click to show/hide)
It plays a video of three old dudes washing and playing with each other, resizes your browser and animates it around the screen so you can't close it. When you do manage to catch the Red X (or try and Alt+F4 it) it gives you a dialog, which when cancelling or clicking OK - will just start the whole ordeal over again. The only way out is Task Manager.
Its a good one to send to friends on IM clients / Facebook etc
