Can someone explain the meme? I’m a little slow.

Human embryos (and probably others) start out female, and grow the male parts a fee weeks later. There is probably someone lurking who can give better details but that’s the gist of it. Thats why men have nipples.

Yeah the Y chromosome doesn’t kick in until later in fetal development. It’s the reason why AMAB folks have nipples, if you’ve ever wondered, even though those nips offer no evolutionary advantage; they just develop before the X chromosome is done doing its thing.

There’s actually a surprisingly small amount of biological information stored on the Y chromosome, IIRC the vast majority lies on the X.