I was trying to move everything out of a folder to tmp (mv ./* /tmp), which was fine. Then I cd to /, and, wanting to rerun the command I'd run right before the mv, pressed up twice and enter quickly...
Well, it failed once it finished moving /bin/mv to tmp. Of course cp, and a lot of other helpful commands come before mv alphabetically.
It wasn't too bad, just needed a boot from a live disc to move everything back, but I still get nervous whenever / and * are in the same command.
Won't make that mistake again.