I walked into the men’s once in a railway station where the doors were propped open and it was very unclear which was which. It was very obvious due to the urinals, so I rapidly backtracked. I then went and used the ladies and met a young man who looked horrified when he realized his mistake. I felt no discomfort or fear on that occasion.
On another occasion, having chosen to use a mixed sex toilet that was empty when I went in, I met a man at the communal sinks afterwards and was surprised just how uncomfortable it felt, knowing only the two of us were in there. I don’t think he was a particularly threatening man, or I’d have walked out, but I wouldn’t choose to use the mixed sex option again if there was an alternative. I think he felt uncomfortable too as mixed sex toilets were relatively new.
If I found an obviously gay man in women’s clothes in there, in a club say (admittedly unlikely now I’m old) I might not feel fear, especially if he seemed friendly. I think it’s not infallible, but some men don’t seem threatening, where others do.
I did see an upper middle aged man walking around my local supermarket one day in a completely inappropriate white, flowery summer dress and heels. If I’d run into him in the toilet, I’d have backed out rapidly as even out in public, he gave me the willies. Might be different if there was also a child or youngster involved as my protective instincts would probably kick in. If I was with a group of terven women, let’s face it, we’d probably point and laugh. That would be the best reaction.
That’s the thing though. I know some women would find all those situations difficult, which is why all men should stay out, but my personal response would be very variable, depending on who else was there and how threatening I found the man in question. I absolutely would not challenge the scary man if I was on my own, so he could continue to say he’d been using women’s toilets for years without a problem… even though he’d sent many, many women running.