This is a simple prank that involves the computer desktop. This is a prank that frustrates the user especially amateurs.
First press print screen button when you are present in the desktop. Then open Adobe Photoshop (or any other editing program), and then crop the task bar in the photo using the crop tool. You can also use the Snipping tool present in the Microsoft windows 7 edition. Then save the photo in jpeg format.
You should right click on the desktop and go to View and uncheck 'Show desktop icons'. We are doing this step to remove the icons, but you can revive them easily. But when you want to recover things just follow the same step.
You can also autohide the taskbar. Unless the user moves their mouse to the very bottom to reveal the taskbar, they won't even be able to click the start button.
Then right click the photo that you recently saved. Select the option "set as desktop background".
Then enjoy seeing your user frantically trying to select something without knowing that they are just photos of the icon!