I don't understand the focus on someone, in your view, lying to you - I suspect we agree that in the scenario you described, it seeming that the person has lied to you about what's in their pants is much less important than the fact that they whipped it out in front of your family. It wouldn't be any better if a man who identified as such snuck into the changing room and did the same thing. I think focusing on criminal behavior is similarly focusing on an edge case

No, under transgender ideology -- "transwomen are women" -- the MtF trans-woman being naked, penis-and-all in a locker room is not a crime. In fact, states that have fully adopted this ideology have made it illegal to expel that trans-woman from the locker room. It is this ideology that I reject. See for instance: https://reduxx.info/korean-womens-spa-forced-to-erase-biolog... https://www.courthousenews.com/after-banning-trans-women-was...

What about this more likely scenario: If this co-worker never did such a thing, they were a perfectly pleasant and normal person to work with, and you only found out they were trans after you or they had left the company and you no longer worked together, would you still be angry they had lied to you - why or why not? Would whether they'd ever gone into a changing room in your presence affect that anger?

Imagine I had a co-worker "Mike" who said they were married, told stories about stuff their wife does around the house, etc. I sometimes asked them about their wife, I told other people, "Oh, Mike, yeah, he's married." Then after he leaves I find out beyond a reasonable a doubt that he was not married, he had been living alone the entire time, etc.

I wouldn't exactly be angry with Mike, I may even have some pity for him, but I would be wary of him going forward. If I met him, I would be polite, and I would neither affirm anything he said about his wife nor would I make a stink about it, and I would try to limit my interactions because I simply could not understand his mind. Was he lying? Delusional? A story-teller? I don't know but it's not really worth it to me to find out.

So it would be the same with the trans person I meet later on. I would simply not use the person's pronouns, I would be polite and neither affirm nor deny their status. I would be wary and limit my interactions because I would, charitably speaking, lack of a theory of that person's mind, and it would simply not be worth by time, energy, and risk for me to try to navigate the situation without getting myself in trouble.

This also is not true. There are numerous well-documented cases of trans people throughout history, and there are long-standing concepts of "third genders" and others dating back thousands of years (see e. g. https://en.wikipedia.org/wiki/Third_gender#Old_World).

There is a big difference between a third gender and a man saying, "I'm a woman because I say so" or "transwomen are women." Eunuchs, eg, were not women, and were not considered to be so. If we want to say that cross-dressing men are a "third gender" that is more acceptable to me than saying they are women and entitled to all the rights and privileges of women and you are fired or cancelled if you say otherwise.

I also should have qualified, as saying "novel in the history of successful societies." Societies in their late stages of decadence and decline have done all sorts of crazy things. Emperor Elagabalus was perhaps "trans" but that was always considered as crazy and bad behavior.