Hmm, it looks like I thought I was being specific when in fact I was being quite vague in my question. Maybe what I should have asked was: is there a systematic set of nonverbal cues such as tone, body language, and so forth, that I can use to reliably tell when someone is being facetious/mocking/sarcastic, as opposed to when they're being serious? This would avoid the need to know the ingroup beliefs ahead of time. I believe that this set of cues exists, since most people seem to get it right the majority of the time*
Just my personal experiences, so take it with a grain of salt:
In the US and Australia, sarcasm generally has a very distinct tone of voice. I can identify sarcasm, jokes, etc. from tone of voice fairly well, even if I don't know the speaker. In Britain, "dry" humor (where the tone and body language mimic a "serious" statement) is more common, but you can still usually identify it based on Adelene's comment above if you know the culture well.
In both cases, the choice of words is still fairly distinct - there's usually an emphasis on unre...
I am beginning to suspect that it is surprisingly common for intelligent, competent adults to somehow make it through the world for a few decades while missing some ordinary skill, like mailing a physical letter, folding a fitted sheet, depositing a check, or reading a bus schedule. Since these tasks are often presented atomically - or, worse, embedded implicitly into other instructions - and it is often possible to get around the need for them, this ignorance is not self-correcting. One can Google "how to deposit a check" and similar phrases, but the sorts of instructions that crop up are often misleading, rely on entangled and potentially similarly-deficient knowledge to be understandable, or are not so much instructions as they are tips and tricks and warnings for people who already know the basic procedure. Asking other people is more effective because they can respond to requests for clarification (and physically pointing at stuff is useful too), but embarrassing, since lacking these skills as an adult is stigmatized. (They are rarely even considered skills by people who have had them for a while.)
This seems like a bad situation. And - if I am correct and gaps like these are common - then it is something of a collective action problem to handle gap-filling without undue social drama. Supposedly, we're good at collective action problems, us rationalists, right? So I propose a thread for the purpose here, with the stipulation that all replies to gap announcements are to be constructive attempts at conveying the relevant procedural knowledge. No asking "how did you manage to be X years old without knowing that?" - if the gap-haver wishes to volunteer the information, that is fine, but asking is to be considered poor form.
(And yes, I have one. It's this: how in the world do people go about the supposedly atomic action of investing in the stock market? Here I am, sitting at my computer, and suppose I want a share of Apple - there isn't a button that says "Buy Our Stock" on their website. There goes my one idea. Where do I go and what do I do there?)