My point is that your definition of "authenticity" seems to include behaviour that is plain inconsiderate of other people.

I think there's a line there. You can wear what you like, think what you like, speak how you like, but only behave how you like up to the point where your behaviour negatively affects other people. If you want to listen to shit music in your own home, you do you, that's fine. But inflicting it on everyone else in a train carriage is not "being authentic" it's "being an asshole". You're not expressing your true self in a brave way that should be admired. You're annoying everyone around you by being selfish. It's a huge difference.