When I was 15 or 16, someone said to me as part of a conversation, "I think you're a bit of a prude." I have never, ever forgotten this, and obviously I've never forgotten it, at least in part, because I'm afraid it might be true. I think about it now because a number of the people I sit with at lunch and dinner talk about sex a lot, and I really wish they wouldn't (although I have been told that I talk about it rather a lot, too). I don't think it's a subject to be discussed for long periods at the table. Also, I've never felt comfortable discussing my own sex life with my female friends; I believe this is a canonical thing for women to do, but I don't do it. If my friends want to tell me about their sex lives as a means of asking for advice, I'm happy to listen, but I just don't want to talk about mine.
And here, people who have never met me and thus are not judging me, I want to defend myself. Because I really don't think I'm a prude - I'm not even remotely prudish in my own private life, which is what I think should count. What I am, not a prude, is a believer in privacy, and also a believer in specialness.
First of all, I think some things should be private. The main reason why I don't like to talk about my sex life with my friends is because I feel it's a betrayal of my partner (& can I just say here that I'm not Fort Knox: if friends want a general verdict, I'll give one. But I'm not one for sharing the particulars); my sex life is also my partner's, and I don't think my partner would like having his sex life shared with my friends. I think a couple's sex life is sort of like a secret shared between the couple. And to keep such a thing private makes a bond; it contributes in part to making a "we."
But even when I don't have a partner, I don't like to discuss sex repeatedly or at great length (tee hee) over the dinner table because I think some things ought to be special. Not talking about sex is like wearing a tie to the ballet. (I think that might be a Buddhist koan.) You wear a tie to the ballet because everything isn't like everything else: some things are special, and you acknowledge that they're special by dressing up, by marking them out. Sex is special, too. You don't talk about it the way you'd talk about baseball, or what you did at work today: you acknowledge that it's special by marking it out in that way. So, in fact, sex is like wearing a tie to the ballet.