Here's mine: When posting on somebody's wall, if you write ">_>" somewhere in the message (it's a smiley), the rest of the post will be cut after the first ">" when you click on the Reply button.
Random game thought :
Why is Bionic Commando Rearmed 2 getting so much hate? We finally get a real game and they're not even satisfied... I'm starting to hate the gaming community so f****** much...