That means neither of the two most tempting responses, correcting people or looking wounded, serves you well.
A better choice is either true let-it-go acceptance, or an answer you can smile through that implies "What an obnoxious thing to say."
For example, there's the versatile "Wow." Or the bewildered "Huh. Why do you say that?" It shifts the burden back to the intruder, and only the obtuse will treat it as a legitimate question. (And when they do: "That was a rhetorical question," then change the subject.)
Question: My parents are very kind, loving people who believe it's rude to speak up for themselves. If relatives come through town and want to stay at their home, my parents allow them to, and cook all the meals for their guests.
One relative makes rude comments to my mother about her decor or the food, which makes Mom cry.
This year, I'll be in town when the rude relative is visiting. I do believe in telling people when they've said something offensive, and am afraid of embarrassing my parents when I speak up for them.
Answer: "When I speak up for them"? In other words, is there a way to make this about you that appears gallant?
I do sympathize, and I don't think you mean to be selfish.
Just as it's your parents' right to take this relative's abuse, it's your right to stand up to it. Just expect and accept the consequences, and be honest with yourself about what you're doing: It's not speaking up for your parents. It's speaking up for you.
E-mail Carolyn Hax at tellme@washpost.com, follow her on Facebook at www.facebook.com/carolyn.hax or chat with her online at noon Eastern time each Friday at www.washingtonpost.com.