edible-underwear
Explanation
The Joke
A man announces to his partner, "Hey honey, I'm wearing edible underwear right now." She responds with interest: "Ooh... show me..." He then reveals what he means: "Technically, these began as cotton underwear, but I've worn them so long that the cellulose in the cotton has hydrolyzed into glucose." In other words, his underwear has not been changed in so long that the cotton fibers have chemically decomposed into sugar.
His partner is horrified, declaring she was not actually interested in edible underwear in the first place and has now decided to never have sex again. Undeterred, he suggests she call him "Cotton Candy" (since his underwear is now essentially sugar). She refuses. He tries "Sugar Daddy?" She refuses again.
The Humor
The comic takes the concept of edible underwear -- already a somewhat absurd novelty product -- and makes it vastly more disgusting by applying real chemistry. The idea that someone could wear cotton underwear long enough for the cellulose to hydrolyze into glucose is scientifically referenced but practically revolting, requiring a level of neglect that goes far beyond mere laziness. The pet name suggestions ("Cotton Candy," "Sugar Daddy") compound the horror by showing the man is completely oblivious to how repulsive the situation is, doubling down on romance when his partner has been permanently traumatized. It is a classic SMBC formula: take a scientific fact, apply it in the worst possible social context, and watch the fallout.