I've never been confused for the opposite gender online, at least to my knowledge. IRL I've been a cashier for a few years and occasionally a customer comes through my line not paying attention and says ma'am or miss. Actually had it happen a couple days ago. A woman called me miss and caught herself, said sir, and apologized. Told her it was okay, it happens occasionally, and said most people don't even bother apologizing. Her response? "Well you look like a girl anyways." Which was very confusing because A: I don't, and B: I had a face full of stubble because I hadn't shaved for a couple days