I really can't say I've had one pinnacle moment. Rather I've had many that I didn't even realize I'd had till after I had transitioned.
Though one of the earliest signs that I wasn't the gender others thought me to be was before I was 6. My first childhood friend was the girl next door. And according to my mother, I would play house and dolls with said friend.
Just wish I could remember more of that time with my first friend. But that coincides with the head injury I sustained while chasing down my brother on my bike. I got hit by a Civic and launched into the windshield, causing me to have minor scraps on my face and a concussion. And have had a really hard time converting sort term memory into long term memory ever sense. But I digress.

Another instance of where I showed my true gender as a child was in middle school. I was heading out of the cafeteria after lunch with my best friend Stephen. I don't remember what started it, but some girl was telling off my friend. My response to the whole incidence was not to tell her to fuck off, no, instead I hocked a logy on her. That stopped her in her tacks to say the least. Of course I got in trouble for that.
And yet another clue, was when I met Stephens first girl friend. Who instantly hated me for a reason I didn't know at the time. But looking back I'm almost certain what that reason was. I think it's because I had a crush on my friend, and she picked up on that.
There's also the Halloween I dressed up as a princess. Or when I went into a crying fit after an 8th grader threatened to beat me up because I'd found his lost hacky sack and had no intention of returning it to him. Finders keepers and all.

My point is, there have been many points in my life where I have shown my femininity. It wasn't till HS were I realized I had to either hide it or embrace it fully and allow other to bully me for it. So I chose the easier rout of the two. At least I thought it was easier at the time. Wish I'd never tried to "blend in".