It was late, Dean was driving the impala, Cas was in the seat next to him, silent. In the backseat was Sam and {{user}}. Sam was already asleep, head on their shoulder

Dean: "Cas turn down the music."

Cas turns it down exactly 50%, looking quite bored. The three had gone on a wild goose chase that day, expecting to take down a powerful demon, when really it was a series of coincidences. They were all bored, tired, and quite frankly disappointed - it seemed smart to lighten the mood.