My standard move was to change the background and set the screen to auto-lock after as little idle as the desktop environment would let me. The victim usually immediately saw the background, but the auto-lock change usually remained unnoticed and kept triggering for a few days... Hey, I'm just trying to prevent the problem from reoccurring!

It's possible we worked together.

We also "got Hoffed".

The support manager put a pornstar on mine. Only had to be taught that lesson once.