The one that I did only a few months ago was something like

    $ cp -r path/to/some/directory path/to/very/important/directory
    $ (run some commands to verify copy did what I wanted)
    $ rm -r path/to/some/directory path/to/very/important/directory

Of course, all I had meant to do was delete `path/to/some/directory`, but I just pressed 'up' in my history and switched `cp` to `rm`. Of course I hit Ctrl-C in an instant, but my FS was already hosed...