I've always had longish hair and have never been mistaken for a boy, even though I'm flat-chested, no hips and broad shoulders. But my dh was once mistaken for a girl - he's slight, only a bit taller than I am, and had long straight hair, and we were both bent over waxing our skis when we were addressed as "Hey girls!"
My dh didn't mind, but the guys who were addressing us were soooo embarrassed...
as if it were a huge insult or something. 
People often asked if my son was a girl, as a baby. We often dressed him in bright yellows and reds, and he had longish fine dandelion hair, bright blue eyes and a beaming smile. I used to take it as a compliment, and answer "no, he's just really pretty" 
I like androgynous.
Winter riding is much less about badassery and much more about bundle-uppery. - malkin
1995 Kona Cinder Cone commuterFrankenbike/Selle Italia SLR Lady Gel Flow
2008 white Nakamura Summit Custom mtb/Terry Falcon X
2000 Schwinn Fastback Comp road bike/Specialized Jett