I find it fascinating that so many people know so much about the penises of people they aren't married to.
In my family, I know my DH is circ. I wouldn't have a clue about his dad, he has no brothers or nephews on his side.
I have three girls, my sister has 2 boys, but I have only changed the diaper of one of them, he is circ. The other, he's technically a stepson, and he came to our family potty trained, so no diapers to change. No reason to really know, because no reason to discuss it with them.
My brother, don't know, again, no reason to ask him, or my mom. My brother has one son, but I don't know because I haven't ever changed his diaper (don't know why though, he's the same age as my other young nephew...I guess I just haven't ever babysat him for long enough.)
Among my friends, there are a few boys, but it's just not something we have ever discussed, so I just don't know. Maybe it's because I have all girls? Since I don't have a boy, it's not something that I have had a reason to bring up or discuss with anyone? Is it really all that common to sit around discussing among parents of boys?