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Yet another simple but great prank that yields excellent results from the right people is making them think their monitor was cracked while they were away. Here's what you do:
1 - Find and download a realistic-looking cracked screen wallpaper, like one of these.
2 - Save and set the image as your background.
3 - Hide all desktop icons by right-clicking on the desktop, hover over "View," then uncheck "Show desktop icons."
4 - Hide the taskbar by right-clicking on a blank section of the taskbar, then "Properties," then the box next to "Auto-hide the taskbar," and finally, the "Apply" button.
5 - Unplug the mouse and keyboard from the system so they can't interact with the computer.
Now you're all set! For added effect, do something like this guy did and eat an apple down to the core, rub some of it on the monitor's screen, then leave it on the desk somewhere in front of the monitor. This will give the appearance that the monitor's screen was cracked by an apple core that was thrown across the room.
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