Noun. Can happen when using a cheap, cold water only bidet in winter. Usually the result of a fine jet of ice water hitting the outer rim of ones exit hole. Can also cause teeth to ache, resulting in a realization that the two holes have more in common then previously thought.
"I just used my bidet I received at the under $20 Christmas gift exchange and gave myself a rectal brain freeze. I also found out I have a cavity."
When someone is being a frigid asshole.
Hey Joey, you're being a real rectal freeze...