Used to describe something that is insanely
cold.
Back in the day, witches were believed to be evil, i.e. "cold of
heart." A witches left tit (or teat) is close to the
heart, therefore a witches left tit is very cold.
Also used to describe an unusually mean or nasty person.
"Stop being cheap and turn up the thermostat, it's colder than a witches left
tit in here."
Canadian
toilet seats in the wintertime.
"Who doesn't love a basket of puppies dressed up like the cast of Harry Potter?! That person is as
cold as a witches left tit."