The sack that holds your "nard
s"... a "scrotum" (abbr. "scrote"), or "ballbag" ("baw'bag" in scotland). Also known as the "wee guys' hammock" since it is the resting place of the little baby machine spermees.
'Watch it, or I'll boot you in the nardsack so hard it'll bust, and you're wee guys will spill freely onto the floor"