Other screw-ups
Many, many years ago when I was young and working in my first job, I was given responsibilty for managing a small network of Sun workstations (one of which was a diskless node). One day I decided I need to clean up /tmp since it was close to being full and causing problems, so I logged on as "root" and entered the command "rm -rf / tmp". Note the significant space!
Control-C followed after about 2 seconds, but there was not enough of the system left to be usable (although I was able to dump the data directries to tape prior to a full re-install).