I have two for you. Hardware related, no simple "hope you had a backup" here ;-)

Back in the early days of the Internet when an ISP meant banks and banks of modems in a small room. When working on a BSDi system I crawled under the table to plug in a SCSI drive. I managed to catch the pull cord for the window blinds in the plug. These were the the old style vertical blinds with the metal beaded pull cord. One spark and the power went out for the entire room. Not a happy day...

Years later I was moving equipment from one ISP in Santa Cruz over the mountains to MAE West. I had done the trip twice already, all I had to do now was get the equipment in the rack and powered on. I had a hand cart loaded with servers from the back of the car and a bag with my laptop and cables is over my shoulder. Its late, in the 2-3 am range, and Im very tired. Im alone and the streets are deserted. I steer the cart towards the handicap ramp and I miss the little bump at the bottom. The cart stops, the servers go crashing down onto the curb. Panic! After what seemed like an eternity of staring at the servers on the ground all showing signs of road rash, I gather everything up and get into the facility. Everything is mounted and up and running, with only some minor rebending of mounting tabs. I escape without anyone knowing what just happened. Months later another admin asks me why one of the servers has a huge dent on the side of it. Had to love that VALinux hardware, dented and bruised but kept running!