Are all etiquette questions on topic here?
I personally don't think so. There's a lot of stuff that's called etiquette but has nothing to do with Interpersonal Skills, and there's a lot of stuff that's so different from case-to-case it isn't even etiquette.
Writing skills for example, were already discussed on meta before, and deemed to be off-topic. So, assuming you're asking about whether or not a formal or informal e-mail can be written in all-caps, to me, that's not about Interpersonal Skills, but Writing Skills. I'd therefore say that the 'etiquette' related to such skills is off-topic on IPS. Your example is furthermore asking whether or not something is okay, which has proven to be a type of question that usually doesn't meet the guidelines for good subjective questions.
As for the traffic 'etiquette', it has a related discussion here. As discussed, they might be good, because there's an interaction between people going on. In that case, as long as the question provides enough details, it might be left open. But as for blinkers on an exit ramp, those are traffic rules, not etiquette. So, I'd say asking whether or not to use your blinker or to stop for a traffic light is off-topic on IPS, also because it's a Should-I type of question.
Your third example is again just asking us whether or not something is okay. I think, in this case, the example is so limited to a specific work-environment that saying this is about etiquette won't fly. In your office, the co-workers might react very angry and it's a major faux-pas, while in another office, people will recognize you were in a hurry and forgive you. I'd say this one should be closed, as it's not so much about etiquette as it's asking us whether something is right or not, which is off-topic per the help center
ask us to adjudicate “right” and “wrong” in a situation or whether something is rude/racist/sexist/[insert other discriminatory terms]. If you are having a dispute with your spouse or coworker, we are not going to settle the dispute for you or give you points to argue. Focus your question on resolving your issue, rather than whether there is an issue or not.
I have seen a few good etiquette questions, mainly focused on, for lack of a better word, dress-codes or understanding the reasoning behind certain etiquette rules. I think a good etiquette question on IPS is possible, but certainly not everything should be considered etiquette and on topic.
One of the things discussed as making a good etiquette question is dress-code, but only when written properly. In fact, the only very good etiquette question on IPS was discussed there:
Does the "never wear white to a wedding" rule of etiquette only apply to weddings attended in the United States?
I think a good, on-topic etiquette question contains a few things:
- Enough evidence that we're indeed dealing with a form of etiquette here
- Asking whether or not the rule applies in a given situation is preferable over whether or not doing something would be rude/inappropriate/okay etc.
- And, as our help-center suggest, it may focus on understanding the rule, on the reasoning behind it, just like a question about a theory or concept might.
This is of course not a definitive list, but at least those are the criteria I see working best for this type of question.