I accidentally untarred archive intended to be extracted in root directory, which among others included some files for /etc directory.
I went on to rm -rv ~/etc, but I quickly typed rm -rv /etc instead, and hit enter, while using a root account.
I’ve had a combination of tab complete and filename spaces lead to things like
rm Some\ Common\ Prefix *at least three times. Instant regret. I’ve now got a pretty good intuitive reflex around this type of thing. You eventually get enough callouses.