'That's what she said' was a running joke long before television, but it was popularised in the United States by Wayne's World and then made defining for Michael Scott in the American version of The Office from 2005 onward. Scott used it compulsively, often at work and always at the worst moment, which turned a simple innuendo tag into a catchphrase. Clipped on its own, the four words spread through forums, videos and soundboards as a standalone punchline that needs no setup beyond someone else's accidental phrasing.