driver picks the music, shotgun shuts his cakehole

A quote made famous for its use in season 1 of Supernatural. Implies that the driver of a vehicle chooses what music they and the passengers will listen to while whoever is riding shotgun must stay quiet.

Sam: You gotta update your music collection. Black Sabbath? Motorhead? Metallica? It's the greatest hits of mullet rock.

Dean: Well, house rules Sammy. Driver picks the music, shotgun shuts his cakehole