I know you are but what am I

Origin: , but dates back at least to the June 15th, 1957 issue of The New Yorker (Vol. 33 No. 17, page 23). In "The Talk of the Town", which was a collaborative effort by the magazine's staff writers: "INTERROGATIVE WISP FOUND IN GUTTER OF MACDOUGAL STREET: 'I know you are but what am I?'" The phrase is often attributed to Pee-Wee Herman. Origin information sourced from Wiktionary contributors (CC BY-SA 4.0).