I feel so dumb when I read kids doing these things. Back in High School all I knew was how I could run arbitrary executable files by renaming them to calc.exe. We also did the classic "take a screenshot of the desktop, set it as the wallpaper, then remove all icons and the start menu" thing.
>>dyingk+(OP)
Another good one on that level was using the Windows keyboard shortcut ctrl-alt-down to rotate the display upside down - totally harmless, but absolutely maddening if you don’t know how to undo it
>>rmorey+kJ
Even better if you combined it with an upside down screenshot of the desktop. So it looked like only the mouse was upside down and all buttons didn't work.
>>gpt5+hU
I think it's a good thing that Ctrl+Alt+Arrow is no longer intercepted by graphics drivers, since IMO shortcuts not containing Win should be handled by apps and not the system.
>>dyingk+(OP)
I told a friend who knew absolutely nothing about computers to go and type format c: on the school only computer and wait for the result. It turned a bit ugly but we're still friend :)
>>dyingk+(OP)
Change wallpaper to some crap. Take a screenshot of desktop. Change wallpaper back and open screenshot with crap on the background in fullscreen mode.