One of my favorites is where Calvin turns himself into an elephant using his transmogrifier (like Hobbes, his metamorphosis is hidden to outsiders) and goes to play with Hobbes in a mudhole. Suzie walks past.

CALVIN: Hey, Suzie, what do me and Hobbes look like?
SUZIE: I dunno. What?
CALVIN: The Republican Party and Tammany Hall! HAHAHAHAHAHAHAAHA!
...
CALVIN: Forget it, Hobbes. Girls just don't understand sophisticated humor.