Immediate Windows Update
I'm a bit sketchy on the details for this one, as I was on of the many victims rather than the perpetrator, but it turns out that the option to test a Windows Update on one test computer is right next to the option to immediately deploy the Update to every desktop in the whole organisation.
Which is why my PC suddenly started shutting down without warning one morning, and when I looked around, everyone else's PC was shutting down as well.
It was like something out of The Matrix (or would have been if the shutdowns had been accompanied by pictures of descending digits and some spooky music).
Anyway an intensive "retraining programme" was apparently arranged for the unfortunate perpetrator (in the sense of "would you like to get some training with another employer"). Bit harsh as AFAIK it was caused by a spectacularly poor UI.