"These are acquaintances and work colleagues who I see on a semi-regular basis, so I have to keep things nice."
Yes, you do, and yet... this wasn't nice for you. In fact, reading your post made me boil, on your behalf. People can be so very rude sometimes.
I usually handle insensitive remarks with humor, with a bit of a sarcastic bite and just enough truth to chase them off and prevent further comments. But, like you, I also like to keep much of my private life, private.
I think that if I were in your shoes, I would smile pleasantly, look them in the eye, and say "How very rude of you." Then I would stare them down and let them stumble out excuses, and if they didn't slink away first, I would quietly walk away. And I would remain polite and smiling and very professional after that, but with a bit of chilly distance. Someone who is genuinely interested in you and your well-being, will find you later, and apologize, or find other things to converse about.
But I don't know how close you are to the commenters, or what your work climate is really like.
I really LOVE the "buy me lunch" suggestion, and the "Bless your heart" suggestion.