Two incidents come to mind. Once, at the local authority where I worked, we had building work going on in our computer room. I was working upstairs when all went dead. I rushed down with others to find that the builders had been hammering so hard on the door that they had triggered the emergency kill switch near it. Half an hour of doing the headless chicken dance and all was back with the world. In those pre outsourced, pre SLA, pre critical indident days there was a bit of a meeting which involved reading the riot act to the builders and all went back to normal. I dread to think what would happen now.
Second was at the same authority but a different computer room. We had to shut down for weekend electrical work. I was doing the Sun boxes while colleagues were doing the Windows stuff. The facilities guy was there to turn off the power when we were done. I had just got the payroll DB server to the OK prompt and typed the words power off when the facilities guy hit the off button at the exact same moment that I hit return. Cue silence and a lot of swearing from the Windows people who had only got half way through their shutdowns.
Beer cos it is Friday.