[4RE KLR]

How about

"Colder than the balls on a brass monkey"

This came about by cannon balls sitting on a brass "monkey" or frame on a ship while at sea. The monkey was so the balls would not roll all over the deck of the ship as it swayed back and forth. When it was cold outside the sailers would to say it was colder than the balls (caoonon balls) on a brass monkey.