It's Always Sunny in Philadelphia first aired in 2005 and became a long-running FX sitcom following a group of self-absorbed friends running a Philadelphia bar. Its cheerful opening music became shorthand online for the show's tone, and editors began reusing the short theme as an intro cue in memes, reaction clips and gaming streams. Because the tune is short, upbeat and immediately tied to scheming characters, it still works as a quick signal that something clever, selfish or doomed is about to unfold.