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Sounds like OP might be a DJ -- they usually wear headphones while mixing so they can actually hear the music over the noise of a party or club.

... and to hear different music than what is playing (cueing the next track, or effects).

To DJ at them.

Because clubs and house parties are loud and play awful music? (Yeah, I know he was the DJ)

He was probably the DJ.

To listen to music. Duh