Really? That strikes me as odd. I mean, I saw my mother and grandmother naked a lot growing up, but don;t really remember their bodies. They had large breasts; I couldn't say how large. Grandma was thin, Mommie was fat. Grandma had light skin, Mommie was dark. Grandma had lots of moles and birthmarks. This is the full extent of my memory of their naked bodies. I remember a few friends' mothers similarly. Weight range, skin tone, markings, whether their breasts were larger or smaller, but not how large, or how small. I remember one friend's mother had really pointy nipples. So, it always strikes me as odd that so many men here seem to know how they compare to other men, especially men they don't know well, such as acquaintances from school, or fellow members at a gym.
Maybe so.
This is precisely what I expect, but do not know. I imagine most men only get to compare their erections to ones seen in porn, and perhaps to a father or brother they've seen with morning wood.
One of my exes had a 10" x 6" erection. We measured it because I kept talking to him about how big it was. He told me at one point that he had always suspected it might be big, because his flaccid hang was more than other guys he'd seen in locker rooms and urinals, but that he'd never been too sure, and that it didn't look very big to him. His experience echoed the OP's thoughts pretty much exactly.