I had one guy..one.. that kept doing this, only he was obviously intentionally avoiding any gender. Problem was he was the head of the organization I belong to.
I came up to him, out of the public eye, and directly addressed his issue. I told him exactly what I don't have, and what I'm not, and please address me appropriately.
In the end some people dislike confrontation, but some people also only respond to actual directly addressing the issue and taking the bear on by yourself. It worked. From then on out, he referred to me correctly.
I don't like beating around the bush with these issues. Some things do require a firm hand and not shrugging it off... I did that too before, and the behavior continued. Sometimes if you ignore it, it also escalates their inappropriate behaviors.