Probably because the genitalia are located in the same place as the urethra, if I had to guess. Beyond that, well, the thing is, all things considered, if I answer questions about what I do and don't do/enjoy sexually, and I'm not speaking on a purely hypothetical basis, I'm really answering for two people. And while I don't mind graphic public conversations about sex (as such) I'm not inclined to broadcast on anyone elses behalf. I will say that, in general, I think it's unfair to ask/expect your girl (or guy) to do something for you that you won't do for her (or him. ) If you don't have a partnership of equals, what you DO have is a problem.