Pustekuchen

Etymology
Early 20th century, originally Berlin slang. . The word on its own is already attested with the same sense in thieves' cant  since 1818, and likely goes back to, used here with a sense along the lines of “you wise guy!” or “you trickster!”. The first component may be, but this appears less conclusive. It may also be merely the verb in the sense “to exhale/snort dismissively”; compare the expression.

Interjection
!


 * 1)  no way!, not gonna happen!, forget about it!