Grandma's Dog

When one is not interested in something until someone else shows interest.

For instance; My gradmother would feed her dog, and he wouldn't want anything to do with the food until you went to take it away. Hence "Grandma's Dog."

Guy 1 goes to eat some pizza.
Guy 2 says "Hey, I was gonna eat that."
Guy 1 "You're such a Grandma's Dog" or "You totally Grandma's Dogged me."