Pastafarianism, the worship of the Flying Spaghetti Monster, is a fake religion created to mock real religions. It was designed to highlight the unfalsifiable nature of religious beliefs and to ridicule their unprovability.
Except, everyone has a religion, even those who declare themselves atheists/secularists and mock the beliefs of others. They too have religious beliefs, for they too believe in unfalsifiable things, they too believe in unprovable things.
This humorous satire takes the weapons of atheists/secularists and directs those weapons back at their wielders, highlighting the religious belief so many of them have converted to and are now aggressively evangelizing today: gender identity. Remember, religious beliefs are unfalsifiable. They present claims that cannot be proven because they don't allow the possibility for them to be disproven. So ask yourself, according to the rules of gender identity, when a biological male claims to be a woman, how do you prove he is not a woman?
You can't—because gender identity is an unfalsifiable claim. It is a religious belief. And it's time for secular society to start treating it like one. But in the meantime, have a few laughs and enjoy the story.