The line comes from Austin Powers, the swinging 60s spy played by Mike Myers in Austin Powers: International Man of Mystery from 1997 and its sequels. Yeah, baby, yeah became the character's defining catchphrase, repeated throughout the films and quoted endlessly in the 2000s. As meme culture grew, the audio clip became a soundboard staple for expressing playful triumph. It endures because the delivery is instantly recognizable, packing flirtation, confidence and retro comedy into two words that work without any visual context.