"To 'nut up' is an archaic phrase dating back to the early 1800's when sailors would tighten the nuts and bolts that held their ship's portholes closed prior to arriving in port. As it became part of the routine for the first mate to call down into the ship's hold for the sailors to 'nut up' when the harbour was in sight, the sea men's cultural language inetivably migrated to their favorite land-side watering holes and brothels. A sea man would call across the tavern at his fellow sailor to 'nut up' if he was failing to control his wench of the evening.

Just as the sailors would 'nut up' the ship to protect against thieves and scoundrels, the term 'nut up' became slang for tightening the reigns on a social situation, locking down the possibility of female conflict, and providing a solid front against the issue at hand, as any good sea man should do."

-- Page 847, line 42 of C. Maurice's Encyclopedia of BullSh*t