No one says, "If you can't explain it to a five-year-old..." because plenty of real concepts can't be explained and understood by five-year-olds. It's usually something like "sixth grader". And I can explain this to a sixth grader. In fact, I have. And they understood. They understood because they accepted prior premises. You don't accept the definition of gender I do. Your definition is nonsense to me and when I explain what gender is, you confuse it with stereotypes.
I'm not talking about how people could use language. I'm talking about how they have and are. I'm not conflating words. I'm showing you that "woman" came to be associated with the feminine to such a degree that feminine symbols signified women. They are literally what you see in public when you identify someone as a woman. You are telling me that you understand semiotics but then showing that you're not and this is the part you're missing and it's everything. It's not possible to move on to your red herrings and slippery slope arguments until this part is nailed down. Instead of arguing anything with reason or evidence, you're arguing by creating strawman arguments.
No one thinks that if a man puts on a dress he becomes a woman in any sense. No one is saying that. No one has done that. And it's a bad faith argument that shows such contempt that it indicates why you're so argumentative.