Breakfast Goblin

Also referred to as a brunch bitch, typically a woman who appears as a strange, shadowy, golem-like creature in the morning, and becomes a friendly and reasonable human during the afternoon. This radical change is often brought about by eating a tasty lunch.

Guy #1: "Why is Janet such a bitch in the mornings but so cool afrer lunch?"
Guy #2 "She's a Breakfast Goblin dude."
Guy #1: "Oh..."