Statement about the temperature being very cold.
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.
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