You know what you should do when you go to like best buy or some overpriced computer place...
If the computer is accessible (no screensaver password) make sure no clerk is around and change the screenname to scrolling letters. Then customize the letters to say "[NAME OF STORE] IS OVERPRICED AND USES SLAVE LABOR" Then password protect it with gibberish.
I don't think David meant for this to be come a how to vandilize a computer that doesn't belong to you. I think encouraging others and telling how to be vandals is some what inapropreate. So I'm gonna lock up this thread.