Whatever else an American believes or disbelieves about himself, he is absolutely sure he has a sense of humor.

White’s line wryly diagnoses a national self-image: Americans may be uncertain about their character, politics, or even identity, but they tend to treat “having a sense of humor” as an unquestionable personal credential. The joke turns on the irony that humor is hardest to self-certify—people who insist on it are often least reliable judges of it. In typical White fashion, the sentence is both social observation and gentle satire: it suggests a culture that prizes likability and informality, and that uses humor as a badge of normalcy and belonging. The remark also hints at defensiveness—humor becomes a safe, universally claimable virtue when other virtues are contested.