I'm sure most of us have done this. We're left alone with a friends computer for a short while, so we change settings on it, and do various other things to annoy them Here's a couple I've done. 1) Changed all of the windows sounds to the Wilhelm scream 2) Changed the screensaver to produce a bluescreen of death 3) The old classic. Take a screenshot of their desktop, remove all the desktop icons and replace the background with the aforementioned screenshot. Any others?