The afternoon is when this story begins to become more interesting. I was on the swim team, as I had been for most of my childhood. I had just gotten moved up to an older age class for 12-14 year olds. I had just turned 12, so I was very much on the young end of the spectrum on the team.
After our first practice, I discovered that nearly everyone on the team had already started to go through the changes of puberty. I had not. My chest was still completely flat and I had no hair anywhere except for the top of my head. I was extremely self-conscious of this, so I got into the habit of changing as discreetly as possible. I would face the locker, practically leaning into it, then change as quickly as possible. Changing in this way exposed my butt to the room, but nothing else.