(Homer is being tested on Santa etiquette...)
Homer: And what would you like, little boy?
Instructor: (sitting on Homer's lap, pretending to be a child) You're not really Santa, tubby!
Homer: (about to attack) Why, you little...
Instructor: Hey, no, Homer! If such an emergency arises, just tell them Santa is very busy this time of year and you're one of his helpers.
Homer: D'oh, I knew that one too.