shame
Explanation
The Joke
A girl tells her grandmother that everyone at school saw her underwear and she will never live it down. The grandmother reassures her with seemingly standard advice: take care of yourself, look out for number one, stay positive, and do not get blue. She says that one day everyone who ever laughed at her will be dead.
The granddaughter asks "So that means you eat nothing but salad?" and the grandmother responds: "Nothing is as good as long-range revenge feels."
The Humor
The comic starts with what appears to be standard wholesome grandmotherly advice about self-care and staying positive after an embarrassing incident. But the punchline reframes all of the advice as being about longevity rather than emotional resilience. "Take care of yourself," "look out for number one," "stay positive," and "don'''t get blue" are all revealed to be literal health advice aimed at outliving everyone who embarrassed her -- not coping mechanisms for dealing with shame.
The grandmother'''s salad-only diet is not about health for its own sake; it is a long-term revenge strategy to survive long enough to see all her enemies die first. The joke subverts the "sweet old grandmother" archetype by revealing her to be extraordinarily petty and vengeful, just patient about it.