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I don't feel entitled to personal isolation from people who might want to strike up a conversation. If I'm not in the mood, I'll just say so.

I feel entitled to personal isolation from schizophrenics, who have a good chance of assaulting me if I look at them wrong. (And did you think screaming and playing loud music was disruptive just to quiet, and not to the aforementioned conversation too?)

You are the problem, not the person you're replying to. When you say 'you must exhibit infinite tolerance of antisocial disruption', the easy response is 'or I could always just leave'.