I'm not sure why peeing is such a sensitive time for people. Maybe it isn't for everyone, but I know my body doesn't like the idea of peeing in front of other people. Not that I never push my boundaries with that.
I wonder if all cultures have "pee shyness" or if it's an evolutionary trait. There's certainly no reason for me to fear being seen urinating. I remember some guy going into a public urinal next to me, and I soon made it clear that this wasn't going to work out. He tried to reassure me that he's "not gay", but I wasn't unable to pee because I was worried about giving someone a free show. It was because... well... I guess I don't really know. My body... my body was just telling me "no".