April Fools' Day
April Fools' Day was an Earth celebration that occurred on the first day of April. Individuals participated by playing practical jokes on one another.
In 2367, while discussing the subject of practical jokes with young Willie Potts, who had become ill as a result of a joke played on him by his brother Jake, 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")