knitting
Explanation
The Joke
A child asks her mother what she's knitting, and the mother cheerfully replies that it's "a sweater for bottles" -- a cute, if slightly odd, craft project. The child laughs, seemingly finding it funny or adorable. The comic then cuts to "later, in the back of a PTA meeting," where a man is seen sneaking a drink from a bottle that is wearing the knitted sweater, using it as a cozy disguise for what is clearly an alcoholic beverage.
The Humor
The joke plays on the innocent double meaning of a "bottle sweater." From the mom's perspective (and the child's), it seems like a whimsical craft project -- knitting a cute little cozy for a water bottle or something similarly harmless. But the punchline reveals the real purpose: it's a covert way to disguise a bottle of alcohol so a parent can drink during boring PTA meetings without anyone noticing. The humor comes from the contrast between the wholesome domestic craft scene and the decidedly unwholesome reality of hiding booze at a school event, as well as the relatable implication that PTA meetings are so tedious they drive parents to secret drinking.