It first appeared in 2006 on NBC's The Office. Then you heard it coming out of your own mouth.
"That's what she said."
The Atlantic is calling TWSS "the best bad joke of the late 2000s"—not because it made our minds dirtier (admit it: They were dirty already), but because it forced us all to think a little harder about what we were saying and how we said it. It's a dumb joke, a cheap trick, but every time one of your friends dropped a TWSS, you had to acknowledge you'd let your tongue slip a little.
Also, it reminded us of the naughty humor lurking in the shadows of our everyday lives. The Office wasn't a stand-up comedy show; it was a sitcom, an approximation of everyday life rather than a tincture of one comedian seeing the yuks in his or hers; and for that reason it was the perfect launching point for the kind of snark that got us second-guessing ourselves.
Puns and double entendres are as old as dirt—The Atlantic mines Shakespeare, Joyce and the Anglo-Saxon 11th century Codex Exoniensis for examples—but TWSS was able to "weaponize" these most elementary forms of wordplay. You didn't have to be a witty person to use it: You just had to know when someone wasn't being witty enough to avoid the pitfall of saying something like, "Well, that didn't take very long."