Importantly though, we emphasised that it was not for him, his (white) son, or his son’s (white) friend to decide what was an effective method of Black people’s resistance. That, most of all, seemed to get through.

Who knows better than White people how to motivate White people to behave better? It's not a matter of "deciding," but counseling. If you want (hetero) sex. wouldn't you appreciate a woman's suggestion as to how to get it?

And then there's the silliness of letting "that word" ruin the evening. You admit that the guy was not "using" the word - language guys would say he was "mentioning" it rather than "using it - and yet you continue to treat him as if he had used it. I understand that the word probably shouldn't even be mentioned, but I also believe that "calling out" a mention requires nothing more than "That word makes me uncomfortable even when you're quoting it." Use is to mountain as mention is to molehill. I think you should have noted your discomfort and moved on. But I'm White, so what do I know?