That means each of us (in most situations!) is the expert on our own sex, right? Because no average person-on-the-street should use their own beliefs, i.e., arbitrary prejudices, to decide in which sex category their neighbor is allowed to live.

I guess there are limited situations in which the relevant expert on someone's sex would be a physician (deciding what the person scientifically is) or judge (deciding what the person legally is). But Giggle hangouts weren't such a situation nor did the Giggle situation involve one of those experts. A person can't just go around declaring what their neighbor socially is and expect their neighbor to have to live by their judgment.

Going forward, I hope T v G serves as precedent.