Yeah, I have been.
I was, I believe, the first active girl on this forum. People assumed for a long time that I was a guy, but I never said I was or wasn't
Also in real life, but nothing for few months now. Sometimes I wear a hat, and I put most of my hair (which is long but thin) under it, or keep it in a double-ponytail. Most of my clothes are pretty gender-neutral. It has happened (more than once and more than twice) that my old history teacher shouted "DONT TALK SO MUCH, BOYS" at me and a guy friend of mine.
My old biolgoy teacher was handing back exams we had taken, and was reading up the names and we were to put up our hands. She read out mine, I put up my hand, and she said "no you're a guy, you can't be Freyja", and read out next name.
Also, when I went out with my ex, people would think we were gay. I wonder who was the lady of the relationship........