I nver made such mistake. But some women have done such mistake when I am in Bath Room. I was just three years back in a conference. I had to enter toilet. A woman also came in. She rebuked me saying that I entered women's toilet. I politely toled her that this was the other way. She just left out relizing her mistake.
I had gone not by mistake but intensionally.But what I did at that time is that kept my wife on the passage to inform that there is a wo"man" inside the toilet.
Never in dreams I can think of doing such a big mistake and if I really do it some day by mistake then I think my senses are not responding properly and there is something serious problem with me and my senses and perception.... :) :)