It's a word play on transposing which is rotation of matrixes and trans-thingy which is usually the gender change from male->female or female->male. This is visualized by the male ♂ and female ♀ symbols, which also look a bit like rotated versions of each other. Excluding any gender-nonbinarity, both functions are involutions, meaning being self-inverse.

(Trans-thingy (anyone got a word for this?) is obviously not a function you can apply on humans like you can apply transpositions on matrixes and there are also nonbinary trans people, so yeah. Still a good Joke tho.)