September 12, 2001. I accidentally shut down an entire production plant. Management didn’t even get mad. They closed the plant for the day, I kicked off the boot cycle (takes hours for the system to be ready for production again) and everyone went home to be with their families. Nobody’s head was on right that day anyway.
EDIT: A few years later I was testing some BigIP configs on a tertiary unit when suddenly the entire e-commerce site went down. Apparently this unit used to be a primary before being demoted and someone (not me) forgot to disable replication, so when I wiped all the rules from my “test unit” I inadvertently wiped all the rules to the production units. Technically it wasn’t my fault but it was still an “oh fuck” moment.