For years, Watterson has corresponded with Berkeley Breathed, the creator of Bloom County, and he has a habit of including insulting little comics with his letters.
Some of the comics got personal. Watterson is famous for resisting all attempts to commercialize Calvin And Hobbes, but Breathed had no qualms about hopping on the Bloom County merchandise gravy train. And when Breathed bought a speedboat with the profits because he wanted to enjoy the fruits of his labors, Watterson drew him cramming money into its engine and yelling at his characters to get back to work while a stock evil businessman does some serious ominous looming.
Later, Watterson drew “a certain cartoonist” as a cockroach trying to convince Hobbes to buy his own boat, and he also drew Opus wanting to slack off on the job and get back to his boat, because merchandise-sale-funded boats is apparently the hill Watterson wants to fight and die on.
Breathed responded in the only logical way he could think of: by drawing Hobbes burying his face in Blondie’s vagina.