At my old uni there were a couple public terminals running DOS, most of the time sitting idle at the prompt. It was bespoke kiosk cabinets only exposing keyboard and screen. One April Fool's I had the bright idea to change PROMPT to something along the lines of "This terminal out of service." - and to increase the confusion, also to change PATH to a non-existent directory, so that most commands wouldn't work and instead flash "Bad command or file name.".

For a couple minutes observed people coming up to a terminal, trying a few things, and stepping away in frustration.

I sure hope administration did restart the terminals overnight to return regular function; normal users were unable to access the power & reset controls.