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Remembering that time I discovered an upward directory traversal bug in a NextStep version of the chown command & wound up owning several dozen user accounts without ever touching a keyboard.
Somehow, my home dir wasn't owned by me anymore, so a sysadmin got root & ran `chown -R arielmt *` in my home dir, but the other user still owned dotfiles, so the sysadmin ran `chown -R arielmt .*` & took a long time to notice it was taking too long to run.
How? Well, FreeBSD's chown(8) manpage says this about -R:
Change the user ID and/or the group ID of the file hierarchies rooted in the files, instead of just the files themselves. Beware of unintentionally matching the ``..'' hard link to the parent directory when using wildcards like ``.*''.
Guess what matched & why it took so long.