But but but we're told all the time that "THAT NEVER HAPPENS" and it's all TRA lies!?
The reality is, natal woman who are butch lesbians, have body types that don't conform to patriarchal standards, or who choose to dress in a way that doesn't conform to patriarchal standards, DO get gender-policed all the bloody time.
Womanhood is hugely policed because of patriarchy. We're operating from a long history of women being told "you're not a real woman because you don't have kids / you're not a real woman because you had a C-section / you're not a real woman because you didn't breastfeed / you're not a real woman because of the way you dress / you're not a real woman because of the way you behave." I could go on and on. And of course lesbians have always been told that we're not real women, that we're freaks, etc.
Women are told they're not sufficiently "woman" all the time, and imo this is a big factor behind the huge rise in teenage girls coming out as trans or non-binary, because societal brainwashing has made them feel that they're not feminine/sexy/heterosexual enough to be allowed to be woman.
Patriarchy is the reason natal men are allowed access to womanhood so easily just by saying the magic open sesame phrase "I identify as a woman", while natal women who want to live as men have to have mastectomies, go on testosterone, adopt stereotypical macho modes of dress, to have any chance of being accepted as a man. Think how many "transwomen" there are who haven't medically/surgically/chemically transitioned in any way and who still present in a stereotypical masculine way yet still expect to be treated and referred to as being a woman. Can you imagine a natal woman, in lipstick and a skirt with long hair and tits in a low cut top, saying "How dare you assume from my appearance that I'm female, I am a transman and I demand you refer to me as he/him or you're a transphobic bigot"? No, of course not. Huge double standard.
The argument "we can always tell" is different. I definitely have met a tiny handful of people where I genuinely couldn't tell. But also, spreading the "THIS NEVER HAPPENS" lie is lesbiphobic, first because it's very obviously a lie (butch lesbians and other women who don't conform to patriarchal standards absolutely do get challenged for trying to enter women's loos, and I'm deeply uncomfortable that a part of MN that's supposed to be about feminism is calling lesbians liars); second, the GC movement has unfortunately been hijacked and used to attack lesbians (by people with their own agenda); and third, homophobia is still VERY prevalent in society.
The statement "women can always tell someone's natal sex" assumes that everyone is operating in good faith. But homophobes do not operate in good faith. I'd bet money that tons of women who have confronted, reported or attacked butch lesbians for using women's loos are perfectly aware that the people they're confronting are natal women, but are just pretending to think they are men, or are faking "having a concern that there's a man in the women's loos" just to be bigots because they think being a lesbian is wrong (or they think woman "dressing like men" is wrong) and they're exploiting all this stuff about gender and toilets because they enjoy having an excuse to harass lesbians and women who don't conform to their version of femininity.
So it doesn't matter if most women can tell from your hands, gait, throat etc that you're a natal woman, if you're a butch lesbian who presents somewhat macho, and someone with a lesbiphobic agenda decides to harass you and accuse you of being a man, there's really nothing you can do short of whipping your fanny out to prove otherwise.