Fortunately my parents never involved me in any conversation like that . . . but . . .
My older brothers and I got drunk the night before my one brother's wedding and the subject eventually came up. What my brother who asked me didn't know was that I knew that his girlfriend provided him some "anal stimulation" when she was blowing him that "blew his mind". So when he drunkenly asked, I said, "Oh, now do we REALLY want to go to that, given that your little brother has big ears and knows what each and every one of you likes?" When my brother started to say something I asked him if he wanted to discuss his girlfriend's "magic finger" and what that might "mean". He quickly changed the subject . . . and two of my other brothers both asked me after that what I had been talking about, but I knew something about each one of them, too, and they backed off.