An Etymological Dictionary of the German Language/Annotated/Schabernack
Schabernack, masculine, ‘hoax, practical joke,’ from Middle High German schabernac, schavernac, masculine, ‘hoax, mockery, scorn,’ also chiefly ‘shaggy (literally neck-rubbing?) fur cap,’ and ‘a kind of strong wine.’ Allied to Old High German ir-scabarôn, ‘to scratch out, scrape together.’ It is uncertain whether the second part of the compound is connected with Modern High German Nacken or with the verb necken. The Middle High German word with its numerous senses may have also meant originally ‘prankish hobgoblin.’ Compare den Schelm im Nacken haben, ‘to be a sly dog’?.