April Fools' Day was a celebration of note on Earth, occurring on April 1st, marked by individuals playing practical jokes on one another.
While discussing practical jokes with Willie Potts, who had been injured as a result of a joke played on him by his brother Jake Potts, Beverly Crusher made the comment that "everybody's played a practical joke on somebody." Willie, however, insisted that he never did, not even on April Fools'. Beverly couldn't believe that he had never "pulled something" on April Fools' Day, to which Willie replied: "What for? It's never funny to the one getting fooled." (TNG: "Brothers")