Gender
Explanation
The Joke
A doctor holds up a newborn baby and announces "Congratulations, it's a girl!" The mother responds that she really does not want to saddle her child with a gender identity before they have had the chance to determine who they are. The doctor then says, "I'm sorry ma'am, but take a look through this magnifying glass that's sensitive enough to detect cooties." The mother looks through the magnifying glass at the baby and sees it covered in cooties (drawn as tiny cartoon bugs). She concedes: "Well, I'll be damned."
The comic takes a contemporary debate about gender assignment at birth and resolves it with the absurd childhood concept of "cooties" -- the imaginary germs that children of one gender supposedly give to children of the other. The doctor uses "cooties" as though it were a legitimate scientific diagnostic tool, and the mother is convinced by this patently ridiculous evidence.
The Humor
The humor works by colliding two very different registers: a serious modern discussion about gender identity and the silly schoolyard mythology of cooties. The mother's progressive position about not imposing gender on her child is presented sympathetically, but the punchline undercuts the entire debate by introducing the most childish possible "proof" of gender -- and having it work. The absurdity of a medical professional using a cootie-detecting magnifying glass, combined with the mother's immediate acceptance of this evidence, satirizes both sides of the gender debate by suggesting the whole thing could be settled by playground logic.