Pee and poo. Just stoppit now. It's piss and shit, two beautiful words so redolent of the stuff/action involved. We've used them since the 1300s. Out with twee euphemisms, say I!

It's quite interesting, however, that grown men and women even in mixed company, even if they don't know each other very well, will often say things like "Hang on a minute, I just need to go for a wee," the norm round here. You don't hear "Hang on, I'm just going for a shit," presumably because most healthy adults will have dealt with that before leaving the house.