The difference in definition between "guts" and "balls"!
Guts - is arriving home late after a night out with the guys, being assaulted by your wife with a broom, and having the guts to ask: "Are you still cleaning, or are you flying somewhere?" Balls - is coming home late after a night out with the guys, smelling of perfume and beer, lipstick on your collar, slapping your wife on the ass and having the balls to say, "You're next fatty.