Sorry for the overreaction; I'm a bit oversensitive on this, I think maybe because of that one "Kiss Me Kate" promo picture I was in that strangers were getting off on.

I think it's clearly meant to be comic exaggeration; stale coffee would not warrant a spanking even in the fifties (unless you were Ianto Jones, of course. Don't trifle with his coffee.)

I've seen it a lot, referred to jokingly, as a comic situation, in stuff from this time period. In "Kiss Me Kate," for instance, she's being a brat, he has had it, she's outraged and the situation is meant to be funny. Also, perhaps it was subtextual for naughty goings-on, a way to get around the Hayes act, "it can't hurt that much" sort of thing.