The line comes from Seinfeld, the 1990s sitcom, where Frank Costanza uses serenity now as a shouted mantra meant to keep him calm under stress. The joke is that he delivers it at full volume, turning relaxation advice into another outburst. Clips of the moment spread through Seinfeld compilations and reaction edits, where the phrase became shorthand for fake calm and barely contained frustration. It remains popular because the situation is instantly familiar: trying to stay composed while clearly doing the opposite.