Funny how that goes with parents. I don't discuss sex with my parents, even in general, biological, purely scientific, impersonal terms, because, frankly, it makes them uncomfortable, especially my mom (my step-dad isn't so uptight, but since mom always hovers around conversations, it's still better to just keep quiet around her). I know she knows what goes on and she didn't mind talking so much when my sister was in college and mom didn't approve of her boyfriend visiting her at the dorms, but it was entirely spoken of in a disapproving tone. What can I say, my mom even gets antsy if I'm talking about breeding cattle or horses.
But, I guess I treat it like any other topic. If it makes someone else uncomfortable to talk about it, I don't discuss it with them, unless they are one of my students, and need to learn the biology of it.