Toilet humor refers to jokes about “rude” bodily functions. Pilkey demonstrates an awareness of his elementary-school-aged readership by using a mild form of this humor, such as when The Inedible Hulk is flushed down the literal toilet. Pilkey also uses toilet humor when the boys create a distraction for Doctor Diaper, sling-shotting the fake rubber dog poo behind him.

George and Harold perform countless pranks that escalate throughout the book, from putting pepper in cheerleaders’ pom poms to turning their principal into an underpants-wearing superhero. George and Harold's love of pranks symbolizes their silliness, sense of humor, and mischief. Although pranks sometimes have negative consequences in the story, they are mostly comedic and bring positive outcomes.