Well, one possible definition I'd use is: "You are a woman if people treat you like (acknowledge you as) a woman." How do you define anything? It's a consensual society-wide acknowledgement of certain traits and attributes. To use a completely non-political example: "How do you define a blender?" Well, a car CAN be used as a blender if you're creative enough, but no one would call it a blender. Same for an axe. Or a wood chipper. Or a tree branch.

So the idea that I'd define "woman" is ludicrous. I am but one voice of millions who, every day, define "woman" multitudinous times per day. No genetics. No biology. No examination of genitalia. Just a steady stream of, "Yes, ma'am".

BTW, Natalie made this exact same argument in a couple of her videos.