Well,
Since you brought it up... I have seen my fathers penis erect.
As a child raised by nudist parents and a step mother whom was a pet in penthouse, so I was used to seeing nudity from an early age.
When I first seen my fathers penis erect he was making love to my step mother and they must have thought I was asleep.
My bedroom was connected to theirs by a large bathroom.
Usually my door would be shut, along with theirs... One night I awoke hearing their sounds of having sex and I realized that I could watch them thru the now cracked open door to their bedroom.
My father has a 8 1/2" long and very thick penis, and I learned to watch their love making by sneaking and looking thru the cracked doorway at nights and I also started masterbating for the first time while watching them.
Later I got to watch my step mom masterbating herself and she eventually caught me masterbating while I was watching her, and this led to other things that happened between us as well.
She had already seen us boys naked and knew we where all large down there flaccid. But the first time she seen me erect she said that it shocked her how much larger we where compared to our daddy. Whom she thought was rather large anyways...
Anyways, Our dad actually has a smaller penis then my brothers and I do.

Grant