But imposing different sex-linked behavioral expectations on people is itself unacceptable social behavior.
I’m aware that the two facts both persist despite their irreconcilability, but so it goes.
You misspelt France
I’m in the ‘not rude, but slightly shabby’ camp. And I say that as a guy who hasn’t shaved in almost a week - one of the things I like about my job is that being a little scruffy isn’t a problem. In fact, I’d put it at right around the same level as facial stubble.
The only circumstance I can think of that would make it rude would be a wedding or other hyper-dressy event. And even then, it’s more that not dressing up for a big event is kind of rude. Not oh-my-lord unforgivable rude, but less classy than if you had.
(I also have to confess that, in a blatant betrayal of my hippie roots, armpit hair kind of squicks me out, and not just on girls, either. If it wasn’t for the unpleasantness of shaving concave surfaces, not to mention ingrown hairs, I might shave myself)
Here, here. I never know how guys manage it. I always feel so sweaty when I’ve got all that hair in there.
I think if we are using the term “rude”, as in Emily Post-ish “manners”, yes. Given that her definition of “manners” (with the lack thereof constituting “rudeness”) is a system of behavior designed to help everyone get along and be as comfortable as possible, then it IS “rude” to expose body hair in a setting and among people where it can reasonably be expected to be considered offensive or inappropriate.
Sort of like saying “Fuck” in front of elderly aunt Tillie or exposing lots of cleavage at a conservative sort of function. Nothing is inherently wrong with either act, and in the proper setting and among the proper people, neither would be considered “rude”. It is all about context, and consideration for other people.
I shave currently, just as I feel more comfortable physically doing so, but I have spent plenty of time not shaving at all. I see nothing wrong or gross about it. But if I were unshaven and going into a setting among those who DO or even MIGHT find it gross or inappropriate, I would not flaunt it. I would cover it up to avoid bothering anyone. To me, manners, in that sense, is more important than making some statement about my personal bodyhair styling choices.
It’s not only women now. For instance, when men where tank tops it’s “not correct” to have a hairy chest. More and more men are shaving their legs and arm pits too.
If you watch basketball notice how many of the players are shaving their underarms. Once you start looking it’s annoying how you can’t stop 
I think Emily Post would probably have said that exposing one’s legs or arm pits in public is unmannerly. Especially arm pits. I, for one, am always surprised when I see women walking around the office in sleeveless shirts. Some of them have been cut so far in that the sides of their breasts were showing. Shell and sleeveless blouses are meant IMO to go under a jacket in hot weather to reduce the amount of layering. They are not meant to be worn alone.
Sundresses are OK at the park, or out shopping, but I personally wouldn’t wear one without a shrug or something to cover my shoulders.
Bottom line, the sight of armpit hair is shocking to most Americans. I’m certain that people will make unpleasant comments about you if you show any. For me personally, the sight of anyone’s armpit is unwelcome, no matter how well groomed.
You have to take clothing into context as well. I have no problem with women not shaving, it’s their prerogative. But, I feel, most feminine clothing and outfits are designed under the idea of modern feminine conventions and aesthetics. Skirts and sleeveless blouses clash with unshaven appendages at the workplace or a formal event; It’s unappealing and uncouth. Yet, shorts and a tank top at a BBQ is fine.
So, if you decide to don an evening gown, please, shave your body to match. Otherwise, wear something more “hairy-appropriate.”
I don’t shave my armpits, but I agree that if ever I were going to be wearing a sleeveless evening gown then I’d shave 'em. I wouldn’t be happy about it, but you’re not supposed to look “natural” in an evening gown. You’re supposed to look fancy, and that means heavier makeup than for daytime, pretty shoes, styled hair on your head, and no visible hair on your body.
I probably wouldn’t ever wear a sleeveless gown though, mostly because I don’t think my upper arms/shoulders look very good! I’d want something with sleeves or a jacket.
I think it’s more of a fashion thing than an etiquette thing, though there isn’t necessarily a strict line between the two.
I was riding on a bus once and a (short) guy with a loose short sleeved shirt was standing next to me holding onto the pole. I was treated to a good, close look at his armpit, all long deodorant covered hairs. It was a horrifying sight. I thought it was ‘rude’, though unknowing, on his part.
If it had been a woman sticking her hairy deodorant encrusted armpit in my face, I would have seriously questioned her mental/emotional/social stability. Or offered her mly seat.
Out of curiosity, would you say body modifications are rude if you’re in a conservative setting? Some tats are in places you can’t cover up, and I don’t think many people would take their non-lobe piercings out just to suit the occasion. So it becomes much more laborious (or impossible) for the tattooed/pierced person to not run the risk of offending someone.
I would say getting a tattoo in a non-cover-upable location is inherently an act saying you don’t care about the expectations of a certain part of society. There is of course more to the decision, but part of the package of ideas going into that decision is that you semi-permanently signal that belief.