I've heard the term both ways. The impression I get is that it's intended to cover a swath of things that harm somebody, either intentionally or unintentionally, but which individually don't seem significant.

It's possible for people to use that intentionally: to deliberately cause offense in a way that they know they can't be called out on. But that wouldn't be significant if it weren't part of a larger pattern where the effect is greater than the sum of the individual events.

Many of those are unintentional, though they might recognize the problem if called out on it. As an example: asking a woman to get coffee for a meeting. In itself, it might be that today you happened to choose a woman; tomorrow it might be a man. She cannot prove that it's sexism without establishing a pattern, which would be an enormous and absurd burden to put on her.

It's even possible that the boss genuinely did choose her at random, but it still echoes with past explicit misogyny and chauvinism in a way that harms her but she can't usefully fight back against it without seeming to blow things out of proportion.

I agree it is a tough problem, specifically because the intention or causality is uncertain. It isn't sensible or desirable to punish good healthy behavior simply because it can not be readily discerned from bad behavior.

What are we to do with your example of the "good boss" who randomly selects a women to have coffee? Never have coffee with women, or all employees because only doing so with men could also be taken as harmful behavior?

At some point, trying to police every behavior on a probabilistic basis has more collateral damage than it is worth. At some point the problem can no longer be productively addressed by punishing behaviors and we have to use other mechanisms for harm reduction.

Slight clarification that doesn't alter anything about your reply: in the "get coffee" scenario I meant it as "go fetch coffee for the meeting". That's a stereotyped role in which women were assumed to be mothers/caretakers to the office in addition to all of their other duties, but which men would think was their primary duty.

He could ask somebody to get coffee without intending to bring up a whole history of chauvinism that you weren't even aware of, but it's also kinda his fault for not thinking it through.

That's just to clarify what I said above, not really a reply to any of the points you bring up. You're right that in the end this is inherently fuzzy. But I do think it's useful for everybody to say "I'm going to do more than just the bare justifiable minimum, because there are real issues out there, deliberate and otherwise."

That's not an injunction; it couldn't be. But it's something to think about, and the people who say "I'm not going to think about it because it's not my problem" are almost certainly the problem.