jailbreak
Explanation
The comic shows a grandfather in a jailbreak scenario. In the first panel, the grandfather tells his grandchildren that he doesn't understand them -- he's never spoken up or gotten angry, and never in his life has he gotten an answer more than 5 words long. His grandchildren are surprised and say they didn't know he was like that. The grandfather then reveals that of course, before that, he had fuel injection systems, knew about full-metal jackets, and could discuss carburetors and the facts of World War II at length. His grandchildren are stunned. Then, 17 hours later, the grandfather is still going, declaring his love for them, while the family begs him to stop. The final panel shows it's too late -- the grandfather has "jailbroken" and can't be stopped.
The joke uses the tech concept of "jailbreaking" (removing restrictions from a device) as a metaphor for an elderly man who has been emotionally reserved his whole life suddenly breaking free of his inhibitions. Once he starts talking openly about his passions (cars, military history) and expressing love, there's no putting the genie back in the bottle. It satirizes the stereotype of stoic older men who never express feelings, suggesting that if they ever started, they'd never stop.