or just leave it up to the girls to figure out amongst themselves.
It doesn't matter what solution you come up with, these turds will never be satisfied. They need a final solution.
This solution could create the scenario, "shit or get off the pot. If you want to go to the bathroom with the girls(or boys) then get the required sex change operation." Hot off the press: "The Association of Plastic Surgeons lobbies for Penis/Vagina signs on public bathroom doors."