Seems like we’ve covered this in another thread, but here goes:
In elementary school we had trough-style urinals. On the first day of first grade the boys lined up to urinate, and of course we looked at each other’s penises.
I noticed the other boys’ glandes were exposed, so I pulled my foreskin back to match. (I never did this at home.) Then I noticed they didn’t close their foreskins before putting their penises away. I knew that would be painful to have my bare glans rubbing my underwear, so I closed my foreskin. Nobody noticed.
Right then I realized what circumcision did to a penis. My mother had told me all the other boys were circumcised, but I didn’t know what that meant until I saw their glandes exposed full-time.
