I ran that once on a system. Good thing I was just working on setting it up. I was talking to a cute girl at work while I was working on the system and meant to type the directory name with the rm -rf <some directory>/* but only typed rm -rf /* and hit enter without looking. She thought it was pretty funny.Pics or it didn't happen.
'sudo rm -rf /*' is the worst one ever. It essential means remove (rm) recursively and forcefully (-rf) every file under '/' (/*) and for those of you who know what '/' is, it's the top directory for EVERY FILE ON YOUR COMPUTER. So it will delete everything while having admin rights to delete any file it wants.