[akoboldfrying]

Thanks for responding. We might be mostly in agreement: I think the employee's concerns that you mention are genuine and important, but I see the root cause being some combination of the customer's and the boss's choices -- the customer being spiteful is the kind of retribution I consider harassment, and to the extent that they act that way because they're confident the boss will reflexively take their side, an abuse of power, though the boss also shares responsibility there. If both would instead behave like reasonable adults, declining an invitation would pose no threat to the employee's job security, and there would be no need to (formally or informally) regulate it.

I realise that that "if" isn't helpful to someone who has to deal with a reality where it doesn't (or even just might not) hold. But the point I want to make is that a culture in which we expect by default that the customer and boss will be reasonable, and shame them if they aren't, is just as possible as a culture where we expect by default that no one should ever ask anyone out at work, and shame them if they do. I often see people express things (like the sentence I quoted in my original comment) that nudge society further in the direction of the latter, but I think the former is better for everyone. Let's nudge it that way instead.