I remember a colleague had every document and a lot of stuff she was working on littered on her desktop. Nearly every little bit of desktop real estate was occupied.

Once, when again she left for lunch without locking her computer, a colleague of ours got up, made a Screenshot of her desktop, put everything on her desktop into the download folder and replaced the background with the screenshot. When she returned from lunch she was very quickly irritated that her computer had stopped working, as she could no longer click any of her files and programs.

It was a blast. And she never let her computer unlocked again.