In high-school we had comp science classes which obviously hardly had anything to do with real stuff. In fact, our teacher was really clueless, so we decided to fool her. I made a tiny app that took a screenshot and set it as its background while being full screen and with hidden cursor. So it basically looked as if the computer was frozen. I also made it so pressing alt+f4 would set the background to a fake BSOD image. Next class we fired it up, the teacher tried everything to unfreeze the computer. She obviously failed, so we told her to try alt+f4. BSOD came up, she tried to fix it by hitting on the side of the PC. That didn't work so she unplugged it from the wall socket. We barely managed to not burst out in laugh, it was absolutely hilarious 😂