one of the most famous tricks in the book (the un-written book) is disabling the ability to click anything on the desktop. this is a very simple, but very effective project. the first step is to find somebody to play this prank on.
the next step is to close any programs that are currently running, so all you see is the desktop and shortcut icons. hit the "prtscrn" (or print screen) key on the keyboard. what this does is take a snapshot of the screen. you can also take snapshots of a particular window (as in, only that window) by holding the alt key while pressing prtscrn, but don't do that because we're in the middle of something.
now, open the paint program again and press ctrl + v to paste the snapshot onto the canvas,which should resize itself if it's not big enough. go ahead and save that image anywhere you want to, preferably not in the temp folder we created earlier as it will interfere with our 1337 screen saver.
once you have the image saved, you can close paint. now we want to remove all of the icons on the desktop. obviously you don't want to permanently delete anything that may be important, therefore the easiest (and safest) way of doing this is simply to right-click on the desktop, highlight "arrange icons by" and uncheck "show desktop icons." now that the desktop is all nice and clean, right-click the taskbar and uncheck "lock the taskbar" if it's checked, then click and drag the taskbar to the top of the screen. right-click the taskbar again and choose properties, check the box that says "auto-hide the taskbar" then click "apply" and "ok." now the taskbar should only appear if you move your mouse cursor around at the top of the screen, allowing you to change everything back to normal later. we're almost done.
right-click the desktop background and choose "properties" followed by the "desktop" tab. use the browse button to locate the snapshot you saved, and apply it as your wall-paper. the last step is to laugh at the next person who uses the computer and gets frustrated over not being able to click anything. just don't let them see you laughing.