I've often been mistaken for a girl. The pathetic part is that it's happened so many times that I've forgotten most of them. The only one I can remember is that a host of a restaurant my mom and I went to accidentally referred to us as ladies. The only thing that made it stand out was how embarrassed he was and how much he apologized. By that point, it had happened often enough that I didn't care anymore.
The thing is, I don't have long hair. I often don't shave for days and have dark stubble. I also, you know, dress like a man. That Simpsons avatar (not yellow, mostly pale) is pretty much exactly how I look.