This Instructable is VERY simple, yet VERY effective! What will happen is:
You hide all of the icons on the victim's desktop. The victim will freak out when they see the computer after you do the prank. This cannot harm the computer in any way at all. Please vote if you like it! =D
Step 1: Icon Wipe Out
First, you are going to simply hide the icons on the desktop. Right click on an empty space on the desktop and hover over "Arrange Icons By" and then click on "Show Desktop Icons". Make sure that the check next to "Show Desktop Icons" is now unchecked. Don't freak out when the icons disappear. :P You are now done with the first step!
Step 2: Wait for Victim to Arrive
Now you just wait for the victim to arrive and freak out! Make sure you are watching because it will be HILARIOUS! I will show you how to undo it in the next step.
Step 3: Undo
After about 2 minutes, you should let the victim know what happened. It is just as easy to undo it as it was to do it. Just right click on the desktop, go to "Arrange Icons By" and then click on "Show Desktop Icons". The check mark next to "Show Desktop Icons" should now have a check next to it. Have fun with this! =D