Here's something I did to a buddy to get back at him for pranking me. If you can get onto his computer without him knowing it, take a screenshot of the desktop. Move the mouse cursor off to one side so it's out of view then push the "screenprint" key. Paste this into Paint or other image program and save it as a .bmp file. Make this image his wallpaper. Now create a folder and copy all his desktop icons into the folder (so you can easily put the icons back on the desktop after the prank is over). Delete the icons off the desktop (but the wallpaper will make it look like the icons are still there). Click and drag the bottom task bar with the start button over to the right side so it's vertical. Go to "start" and "settings" and "taskbar and start menu" and hide the taskbar. Now you have a bare desktop with a image of his old desktop. He will click on the start button or icons and nothing will happen. It will drive him crazy.