I noticed that several people mentioned that pretty young women are an exception to the "no-conversation rule" so popular on FT. I now pity the pretty young women who probably can't enjoy a quiet flight without having some nerdy, fortysomething systems analyst or actuary trying to chat them up!
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I generally just enjoy the peace and quiet (if alone) or the company of the mrs. (if travelling with her). That said, I am always happy to talk to neighbours, especially on int'l flights where they are never from my city, although I really never initiate the conversation - even if they are pretty young women!