"Spaceman Spiff: Interplanetary Explorer Extraordinaire!" is a short story at the beginning of The Calvin and Hobbes Lazy Sunday Book. It features Calvin being punished for his antics as the intrepid Spaceman Spiff.
As the story begins, Spaceman Spiff is shot down over an unknown planet by a Naggon mothership. In reality, this is his mom throwing him out of the house for messing around with a water gun. As Spiff plunges to his doom, he takes evasive action by attempting an emergency landing. He survives, and begins to try and find help as he exits his craft. Calvin dusts himself off while giving an annoyed look.
Exploring the planet's surface, Spiff spots a mysterious figure atop a hillside, and hides behind a rock. In reality, the figure is Susie. When the alien (discovered to be a "Bat-Webbed Booger Being") attacks, Spiff fires his zorcher (Calvin's water gun) at the monstrosity, but to no avail. Back in reality, Susie is now soaked, and she storms off to tell Calvin's mom (i.e. the Naggon). Spiff wastes no time in making a speedy getaway as the giant Naggon materializes and lunges after him.
Leaping into a crevice, Spiff readies a Demise-o-Bomb, in reality a water balloon. As the Naggon rounds the corner, he heaves the bomb at the menace. But the Naggon is only stunned, and Calvin's mom becomes soaked and furious. As he tries to ready another bomb, he is captured by the Naggon.
Calvin's mom recounts what happened to Calvin's dad, who goes up to Calvin's room to have a talk. In Calvin's mind, the room is a Naggon dungeon, and as Spiff readies a water bucket trap for the approaching Naggon King, he chuckles that "soon our fearless hero will be free again!"