Not a specific thing, but since around age 5 or 6 (possibly earlier) I was quite jealous of girls clothes, especially girls wearing cute dresses. Which is what lead me to start crossdressing around age 15.
I had no real interest in dating girls (despite the fact that my only sexual experiences were with women & I identify as bi now), and hadn't realized my attraction to guys yet. Even when I did realize in my 20s, I still never had any relationships with men because I had no interest in being with a guy as a guy.

Around the age of three or four. I told my sperm donor at the age of four, I should have been a girl. I recall the impact of foot on chest, the short flight through the air to the bottom of the stairs and the time in the hospital. I kept it private from then on, when I was 20 I went to the doctor because did not feel right, did some tests my E was 54 pmgl and my T 425 so he started me on Testosterone. The feelings did not go away... the only silver lining for me is I was not attracted to men, still am not. Got married, divorced, came close to coming out 7 years ago, mother died the day before I was going to tell her so did not need the rejection from my partner and the loss of mother. Move forward 6 years and told my partner, she has been 100% amazing on this journey.