Step 1: Prank 1: The Impossible Desktop
Step 1: From the regular desktop screen of the computer, press the "PrtScn" button on the keyboard. This takes a snapshot, or screenprint, of what is on the screen at that moment.
Step 2: Open Paint (Start > Accessories) and either select Edit > Paste, or press Ctrl + V to paste the screenshot into Paint. Then choose File>Save As and call it anything, but change the file type to .jpg, and save it to the Desktop.
Step 3: Close out of Paint, and back on the desktop, Right Click and create a new folder, of any name. Set it to one edge. Any icon on the desktop that doesn' t have a white square with an arrow is an actual file or program, and can be moved into this folder. The rest are icons, which once you move into the folder need to be deleted off the desktop. You can remove everything from the screen EXCEPT the Recycle Bin.
Step 4: Right click on the Start/Taskbar, and uncheck "Lock the Taskbar" if it is checked. Now, if you put your mouse over the top edge of the Start/Taskbar it'll turn into a double ended arrow. Drag it down until there is no Start/Taskbar on the screen.
Step 5: To finish up, right click on the now empty desktop, and set the screenprint picture you took to be the wallpaper and walk away.
The Result: Your target will not suspect anything is wrong with their computer until they go to click on something. Anything really. The only responding icon on the desktop now is the Recycle Bin (if they try to move it, they may figure you out, but who ever messes with the Recycle Bin?). Once you've had your laugh, and maybe taken a video, undo your damage before your mark loses it.