freeze the balls off a brass monkey 

Statement about the temperature being very cold.

Background:
A brass monkey is a naval term for the holder that holds the cannon balls. It was made of brass and the cannon balls were not, so when it got cold enough, the two metals would contract by different amounts and the cannon balls would no longer fit properly in the holder and thus fall off.

Person 1: Holy crap its freezing in here.
Person 2: Yeah, its cold enough to freeze the balls off a brass monkey.

freeze the balls off a brass monkey by PlaceHolder August 11, 2004

freeze the balls off a brass monkey 

A reference to extreme cold. According to the United States Navy Historical Center, this is a legend of the sea without historical justification. The center has researched this because of the questions it gets and says the term “brass monkey” and a vulgar reference to the effect of cold on the monkey’s extremities, appears to have originated in the book “Before the Mast” by C.A. Abbey published in 1857. It was said that it was so cold that it would “freeze the tail off a brass monkey.”. The Navy says there is no evidence that the phrase had anything to do with ships or ships with cannon balls.

The first taxi man George encountered in Brooklyn said, "It is cold fit to freeze the balls off a brass monkey."

freeze the balls off a brass monkey by Vigfus April 27, 2016

Freeze the balls off a brass monkey 

Navy phrase for canon balls. The balls are placed in a round structure called a monkey. The plates had indentations to hold the balls on the bottom layer in place. The base was made of brass. When brass gets cold it contracts and the balls displaced.

It is so cold it would freeze the balls off a brass monkey.

Freeze the balls off a brass monkey by WxDub December 19, 2016

freeze the balls off a brass monkey 

The cannon balls on a man o' war were stacked and held in place by a brass ring on the deck known as a brass monkey. In cold weather the sea spray would turn to ice thus freezing the cannon balls together and onto the ring.

Hence the expression "It's cold enough to freeze balls on a brass monkey" or simply "brass monkey weather". Note that the correct phrase is "on" NOT "off" a "brass monkey". The expression is often corrupted to hint at an association with a man's testicles balls

freeze the balls off a brass monkey by TimB June 12, 2005