Most embarrassing command line gaffes ?
davidw: When I first got a 'portable' computer with Linux on it, in 1996, I was trying to use 'tar', but didn't remember the right options to pass to it, and wasn't on line (so no irc or what passed for search engines at the time).  Those days, the man page wasn't very helpful in showing the 'commonly used' options, so somehow I ended up with the partition specified, and overwrote the partition.  Oops!