A couple of decades ago, we were showing the new DBA around the datacentre and he logged onto the production server console - he hadn't got his laptop yet - and checking out his permissions, etc. He went to logout, but instead of clicking on "logout" the idiot moved the cursor to "shutdown" and we weren't fast enough to stop him. Luckily it was a cluster and failover worked so users had a temporary blip. He never really lived that down...
A few years later, at a different vendor, a hardware engineer was walking towards the DC door carrying his toolbox and various spare parts and reached out to press the door unlock, but for some reason known only to themselves, an idiot had put the emergency power down near to the door - and the engineer pressed that by mistake. Cue suddenly silent DC and sounds of panic as the helpdesk was swamped with calls from 5-6 councils and a few businesses...