In translating-interpreting Berlinerisch German to English text I came across the expression "Haare auf den Zähnen" in a paragraph about what the author describes as need of early Berliners -- who came from all parts of Europe; France, Switzerland, Holland, Bohemia, Silesia, Poland, and the Mark, and who had left those countries as the enterprising, determined, and energetic elite -- that those who wanted to assert themselves needed to have "... their elbows and mouths next to their brains". My standard German source is a cold-war era book which has a chapter on the Berlinerisch dialect; the context of the expression is the lead sentence in a paragraph:
»Daß die Berliner Haare auf den Zähnen haben und man bei ihnen mit der Delikatesse nichts weit reiche, hat bereits Goethe festgestellt. Diese Haare aber brauchten sie auch. Berlin war Kolonialland ...«
Coincidentally, a second question is where geographically would have been (or still is) the region known as "the Mark"?