Stuff a bit of tissue paper in your ears.
Dead serious! It reduces the volume but you can still hear the music OK, and even people talking (they have to shout to be heard over the music anyway). I suppose some smart-arse will say it doesn't cut out the dangerous frequencies or something. If so perhaps proper aviation ear plugs would also be OK for this.
If you roll the tissue up right you can take it in and out as required, and even adjust the volume. Simple but effective. And you don't have to look like a nerd...