George Clooney, along with having a face that looks like it was carved by angels with OCD, is also an avid prankster and has no qualms about pranking some of Hollywood’s biggest stars.
When he and Brad Pitt were working on Oceans 11, in response to Pitt telling the crew to not make eye contact with him, Clooney put a bumper sticker on Brad Pitt’s car saying “Small penis on board”. Because even A-list Hollywood stars see the inherent beauty in a small penis joke.
Clooney’s pièce de résistance though was the time he spent weeks secretly cleaning out his friends cat litter box. His friend who became increasingly agitated that his pet hadn’t pooped in three days took it to the vet, which only resulted in more poop for Clooney to secretly clean up. After several more days of this Clooney crimped out a human sized loaf into the cat litter tray and pretended to have no idea where it came from.
So yeah, that’s where Family Guy stole that joke from, see, they don’t steal everything from the Simpsons, just most things.