The first time it happened we were rather confused.
After that it became a running joke that the computer knew when we were stressed and would offer us a selection of mixed drinks.
IT managed to get the number of times it happened down but it never went away entirely.
I buried several Easter Eggs in the Windows application I wrote for a certain unnamed retailer that all of you would know.
It was in their retail stores but the application was only run by store employees in the back. They were harmless and easy to install.
One animated egg was from a basic routine included with the development software. I gave it a few enhancements.
Later I gave one of their help desk guys a guide, over the phone, on how to access them.
A couple of guys on the development team were aware of the keystroke combinations (which usually included a mouse).
I doubt the software is still out there now.