Regarding the phrase “Cold enough to freeze the balls off a brass monkey.”
I have been told that a brass monkey is (was) a contraption used on a sailing ship to hold the cannon balls. Brass, so as not to create sparks which might set off an explosion. In extremely cold weather the contraction of the brass woud allow the contraption to come apart and drop some of the cannon balls. So this really has nothing to do with a primate.
LINK TO COLUMN: http://www.straightdope.com/columns/read/2983/is-it-possible-to-freeze-your-cojones-off