“Socks and sandals. Those really are the two genders.” Variation for follow up: “Damn call me non-binary then”
Two related things are brought up and presented as being “the two genders”. First saw this as a tumblr meme – cannot remember the original. Originally the “two genders” notion was from some right-wing conservative person trying to invalidate queer people, but the argument has been reappropriated to be humorous.
This joke is usually told within queer circles where the notion that there are only two genders is already funny. Usually the two things being distinguished are part of a similar subculture or part of adjacent subcultures. Alternatively, the two genders are almost identical things which can start some heated arguments or spiral the conversation into unexpected directions. The current  college generation age, within a liberal arts setting, also uses the word “vibe” quite a bit, and the two genders joke is often used in conjunction with establishing and identifying vibes. When this joke lands in a crowd, it is quickly designated as a safer space for anyone queer, which more often than not brings about good vibes (safe vibes are good vibes). It’s also a way to tell if you need to leave the room because the people in it might be intolerant to the point where you [a queer individual] might prefer to be elsewhere.