Sometimes at work while I'm checking out people's items I whisper to myself. "Oh god, what have I done."
You should see the people's faces as they frantically look at the monitor to see where I -blam!-ed up. Then I scan the items quicker so they can't read fast enough. Then they get all freaked out and spend an hour reading their receipt before they realize that nothing happened.
So what do you guys go to screw with people?
-
I once used a friend's computer account at a school computer while he was using it and whatever one person did, it happened on both screens, that was a fun day having him explain how his computer was possessed/hacked/crashing to the computer teacher with the both of them watching. Eventually had half the class watching the victim computer and the other half with me watching the chaos unfold.