I'm an American in Japan. Here girls don't need to sneak into the boys locker room. At the sento (public baths) they're unbelievably laid back about girls wandering into the male changing room. I was at my local sento yesterday, and there was a group of school boys in, eight of them, about 15 years old. Evidently there were a two girls from their class in the female side, because they finished early and just came fully clothed into the male changing room to wait for the boys (the changing rooms are brightly lit, and there's TV and games machines, drinks machines). They were gesturing through the glass door into the bath room for the boys to hurry up. And out came the boys, of course stark naked (towels are not allowed inside the bath room), , and in no hurry at all. They were there about 10 minutes, getting dried and weighed (the girls were sitting there guessing how much they thought each boy would weigh), chatting away to one another and to the girls, with their p enises and bare bottoms in full view. Nobody batted an eyelid. The other customers ignored them, and the attendant - a middle-aged woman - was joking about something with them instead of telling them to get out. It's very odd to American eyes.