Du Doch Nicht!! is what German WWI ace Ernst Udet painted on the tail of his airplane. It’s not easily translatable into English; it’s sort of a really strong statement of “Not you!!” More idiomatic translations could be “Definitely not you!”, “No you don’t!”, or “You and what army?”
Several years of German language classes were not enough to clearly understand this idiom. A German friend, when asked, also didn’t know. Perhaps it has gone out of style in the past 100 years of German. Or perhaps it was the kind of idiom that is known in drinking establishments and not official grammar books. One has to wonder what Ernst Udet expected English- and French-speaking pilots to make of his message. Though probably a pilot of any opposing nation could guess it was not intended to be complimentary.
After WWI, Ernst Udet became a friend of Eddie Rickenbacker the American ace, and Udet is mentioned cordially and respectfully several times in Rickenbacker’s autobiography. Ernst Udet was quite a colorful person, and there are several blog posts about him.
It seemed to us that the obvious use of this phrase of Udet’s is on a bumper sticker for the driver behind, honking at one’s car, to consider. So Ewan has put a Du Doch Nicht!! bumper sticker design on his CafePress shop. (Warning: we have had bad experiences and are not sure that what you see on the screen CafePress is what you get. Buyer beware.)