[Coda]

Quick set of bullet points:

* No, physical sex has absolutely no ties to personal gender beyond just a statistical correlation that most people physically male are also male-gendered and most people physically female are also female-gendered. The exceptions aren't necessarily a "rejection" of the physical sex.

* While older feminist theories thought that gender was a purely social construct, that's just as naive of a view as the thought that gender is purely physical. Both extremes fail to account for a LOT of people.

* You will find that most of those 6 billion people actually AREN'T "interested" in their gender. They just live their lives as they find comfortable, rarely thinking about the role their gender plays.

Gender is a complicated thing and there are few generalizations that can be safely made without alienating or omitting some people. The most important thing is to respect those who you meet.