For my own future reference (because this is not, alas, the first time I've engaged in this kind of stupidity) what I *should* have said
(and failed at saying,) and I should have said it in a post of my own, or at very least a top-level comment, rather than singling some poor random commenter out to get all my pent-up headdesk, is something like this:
Hi! I've heard a lot of people saying that "miscegenation" is an American term. This is wrong. It is a white supremacist term. Wherever there are white supremacists speaking English, people are using that term. If you don't believe me, you can try using Google to find out what people are saying in your country about white supremacy, and I will bet you two months jf paid time, they will be using that word fluently. You can also check your dictionaries, if you still trust them at this point: none of them will mark the word as regional or dialect. None of them.
That is why this term is so inarguably offensive: it is associated solely with white supremacism, and it is used everywhere in the English-speaking world to refer to white supremacism. To claim that it is a regional dialect term when it is not reads as an attempt to downplay the power that this word has - which was, after all, the problem in the first place.
That is not what actually came out of my keyboard before, though, and what I did say did nothing to help the situation. That was totally my fault, and I should have thought more before I posted it. (Also, what I did post was way more tl;dr than this, which may be hard to believe.)
Also, I was trying to plot a fic where Dr. Cox and Dr. House have to switch jobs for awhile for some reason (like, say, a stupid bet), but it keeps just ending with Dr. Cox saying, "Oh look, Greggy! I'm better at your job *and* at my job! That's a surprise! I'm going home to my beautiful ex-wife and extremely intelligent son now. Why don't you limp off and I'll see if Dr. Kelso can get you 'company' tonight on his frequent loser discount?"
...but I like House. :(