The guide on how to ruin your friend's wallpaper: Take a screenshot of their normal wall paper, with their applications and files normal. (Windows: (windows key) + Print Screen) (Mac: I dunno) Move the files over 1 unit, and take a screenshot after each move. (Repeat this step a ton of times until the screen is fully covered) Result:
the trick to really ruin someones desktop is to move all of their icons into 1 folder and put it down in the corner. open some random app and have it not in full screen, screenshot the desktop, and set the resulting image as theie background. it is so funny watching people trying to close the app, and then realizing that it is their backgroung XD