What Should I Have Said?

My new boyfriend lives with his parents. He's normal, just saving money for a house.
Recently, I was at his house and his mother and I were chatting alone. Out of the blue, just randomly tells me how big he husband's dick is, then asked if my boyfriend was bigger. I was instantly sickened by her question, and ended the discussion with, "That's a really inappropriate question about your son, and I am going to pretend you didn't just ask me that." I gave her a look like, you're fucked lady.