Emergency power off and BT engineer
I worked at an investment bank in the 90s. Around the walls of the dealing room were a number of emergency power off switches. They looked completely different to the light switches and were not located near any light switches.
A BT engineer was sent to fix some issue and whilst in the dealing room, he manged to lean or brush against one of the emergency power switches, turning off every piece of equipment in the dealing room. He was promptly escorted out.
Some months later, the same BT engineer came with a colleague, to address some issue. On entering the dealing room, he said to his colleague "The last time I was here, I shut everything down because I accidentally pressed one of these buttons." He pointed at one of the switches, touched it and shut off the power again. Suffice to say, BT were told that this particular engineer would never again be allowed into the building.