It was tights, at first, that really did it.
I loved them; I thought girls legs looked so cool, and at nine years old, I was insanely jealous.
For some reason, Mom thought I only liked black or dark blue short socks. Actually, I loved my soccer socks most, because being a shrimp, I could pull them up to the tops of my legs even during games if it was cold, and they'd look like tights. Other boys did the same, and I wished we could do it all the time.
I was "forced" to wear them as part of a school play; I had to be Peter Pan. I was secretly thrilled, while at the same time, of course, I had to present an "Oh, no, not tights!" defensive front to keep my peers and mother from knowing how I really felt.
Mom knew, though. Probably my little kid-boner gave me away mostly, but hey, I couldn't help it. She made me wear the outfit at home "to get used to it", and she undoubtedly noticed me asking if I "had" to wear my costume during the evening.
The outfit was a pair of green tights, a pair of plain moccasins with raised cuffs, a tunic (the 'skirt' of which barely covered a quarter of my upper legs!), and a felt hat.
She bought a few extra pairs with no explanation, and for the next couple of years, tights became a fairly regular option of clothing for me.
They felt awesome no matter what they were worn with; totally exposed with just a T-shirt (this was my favorite before-bedtime outfit), because I could see (and show off?) all my legs in there colorful glory, but also under a pair of jeans (Mom supported me wearing them in winter); I never got so used to them that I'd not notice I had them on, under my jeans or overalls at school, because I could feel my pants sliding over them (the tights were all a plain cotton, and I wore longer plain white sports socks over them).
I still love them to this day.