sleepover
Explanation
The Joke
A child excitedly announces that at her slumber party, the kids are going to "stay up all night by drinking coffee mixed with soda, and maybe watch a movie!" An adult (likely a parent) responds with a counter-proposal: "Why not just do what you and your kind are about to do? You'll never accomplish most of the things you consider valuable." The comic then cuts to "5 seconds later" where the children are shown sitting in silence, apparently having an existential crisis. The final panel shows the child looking disturbed, having been traumatized by the adult's nihilistic observation.
This was part of the "Soonish" bonus comic series. The strip plays on the contrast between childhood excitement about trivial activities and adult existential dread.
The Humor
The comedy derives from the brutal juxtaposition of innocent childhood joy with crushing existential nihilism. A slumber party is one of the most carefree experiences of childhood -- staying up late, drinking sugary beverages, watching movies. The adult's response completely destroys this innocence by introducing the concept that most of life's ambitions go unfulfilled. The "5 seconds later" cut showing the children sitting in stunned silence is the visual punchline, demonstrating how quickly existential awareness can demolish youthful enthusiasm. Weiner often mines humor from adults inflicting philosophical despair on children, using the contrast between innocence and existential dread as a reliable comedic engine.