A bit late but I just remembered this story.. at my college the people in the IT department always watch for when another professor or student leaves their computer unlocked and then change their wallpaper to something funny (e.g. my little pony). One time the instructor from the class before mine left their machine logged in and my professor asked the class "what should we do?"

I suggested he modify the chrome shortcut on the desktop and change the path to 'C:\windows\system32\cmd.exe /c shutdown /r /t 0' then pin it to the taskbar. And he did it.

I wasn't in that class but I heard that she clicked it 3 times before she figured out what was going on. She never fixed it the whole rest of the quarter (simply launching chrome from the start menu) and would occasionally forget and click the taskbar icon and go through the whole thing again.

As fate would have it I got 2 classes with that instructor the next quarter. We're friends so it's all good but I still get flack about it and I don't dare leave my computer unlocked xD