It's rude to turn down people's music mid-song.
Vance bought beer and has arrived to an energetic dance party.
Vance wants to tell the party goers that there's beer.
Vance waits for the song to finish then tells the party goers there is beer.
Vance turns down the music to tell the party goers there is beer.
The party goers will be receptive to what Vance has to say.
The party goers will be annoyed with Vance and not listen to him.