This works better if you have music with a good beat playing.
1. Find a dancing banana. Here's one:
2. Right click on the banana, hit save picture and save as a .gif (should be already by default.
3. Right click on your desktop and go to Properties, then Desktop, and set your desktop position to "Tile". Hit okay. (This may screw up your background. Don't worry, we'll fix that shortly.
4. Go to the folder where banana was saved
5. Right click on the banana file and go to "set as desktop background"
6. Close/minimize all open windows
7. Enjoy the madness.