How I Met Your Mother premiered on CBS in 2005 and ran until 2014, with Neil Patrick Harris playing Barney Stinson, the suit loving friend known for catchphrases and elaborate schemes. What Up became one of his recurring greetings, often delivered as a confident entrance line rather than a casual hello. As clips from the sitcom circulated on social media and soundboards, the phrase detached from specific episodes and became a reusable reaction for arrivals and reveals. Its familiarity and exaggerated delivery keep it popular long after the series ended.