[poncho_romero]

You can simply decline the conversation. It's not as big of a deal as you are making it out to be. I'm not saying you have to actively opt into social interaction, whatever that means. I'm saying its reasonable for others to offer social interaction if you're in public.

[saghm]

"You can simply decline the conversation" and "it's not a big deal" are entirely subjective and based on the assumption that being extroverted is normal. Your rules of etiquette are that I need to go out of my way to give people the opportunity to talk to me so that I can tell them not to rather than just signaling to them that I don't want to (which saves us both time and lets me quietly enjoy some music on the meantime), which is just bizarre.

[poncho_romero]

Your preferred default is also entirely subjective. I'm also not an extrovert. My friends all acknowledge my extreme introversion.