"Mommy, you really need to be a big girl and stand up when you go pee."
Like I need to say it, but this was said when HRH walked in on me just a few minutes ago. That'll teach me to not lock the door. My previous response to his question concerning why I sat down had simply been "because I'm a girl."
Despite untold visits while I'm showering, changing, peeing, etc. as well as my own innate immodesty, apparently further explanation of basic plumbing is required.