Very interesting that I had a very similar reaction from my son. He was 9 and I was trying to be non-chalant and was telling him about the technical details of sex on the way to Little League practice. After awhile he put up his hand and said “stop, that’s all I want to hear right now.”
That night as mom tucked him into bed he disgustingly said to her “you let dad do that to you FOUR times?!
I can’t remember how old our son was, but upon hearing the basic gist of it said, “Well - I’M never doing that!”