Take a screen shot of your desktop (by clicking SysRq button)

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And then paste the image to paint and save it as Jpeg image format . Then open the image of your desktop and make it your desktop wallpaper. Now hide all the icons from your desktop
( Right click > arrange icons by > Hide desktop icon) . Also unlock the taskbar. Now your desktop will look like exactly same like before but everyone will be fooled whenever they try to click any icon. You can do this trick on your friends computer and enjoy the fun show