This article is from the Kurt Vonnegut FAQ, by George A Cooley email@example.com with numerous contributions by others.
Well, IMHO, it was this one, from Corddry (firstname.lastname@example.org):
> Does anybody recognize this quote from a Vonnegut novel?
> "Go take a flying fuck at a rolling Karass! Go take a flying fuck at
> the Dupraaaaaaaaaaaaaaaaaaaas!"
> I think it was in a book called "Venus in the Half-Shell" by a guy named
> Kilgore Trout which is actually Steven King's first pen name under which
> he published "The Body" which was made into a great movie called
> "Slaughterhouse Five", starring Karen Black, Bruce Davidson, and a man
> called Rory.
Then again, I suppose I could be wrong. :-)