> Have you ever left your terminal logged in, only to find when you came back to it that a (supposed) friend had typed "rm -rf ~/*" and was hovering over the keyboard with threats along the lines of "lend me a fiver 'til Thursday, or I hit return"?

Wow that is really nasty, the most we did was put confusing backgrounds in, or cronjob a say "xxx is yyy" and have a laugh in the next meeting :)