I have just been given a facsimile of a very remarkable manuscript book, in which a father and son in 16th-century Augsburg documented - with beautiful colour illustrations - the outfits they had worn throughout their lives, and the occasions on which they had worn them..
On first dipping into it I was startled to read Schwarz Senior’s caption to a picture (image 13-14) of him on horseback, aged 15:
In meynem synn bei beser esel, und mainetz spitzig mit der reuterey, wan mich mein vatter in seynen gescheften auf Minnichen schückt.
In my mind a bad ass [donkey, not bottom] and very keen on riding, when my father sent me to Munich in his business.
There’s no doubt that beser here is modern German böse, ‘bad’; the word, so spelled, is used elsewhere in the text in unequivocal contexts (as is Esel). Whatever the precise connotations of böse Esel the phrase can’t have been worse than mock-derogatory, as the text as a whole implies that young Schwarz was happy to be sent to Munich and thought well of himself.
If the similarity between böse Esel and badass is is a coincidence, it is a striking one. Is it possible that the phrase continued current in German into the mid-20th century? If so, 1955 , around the end of the ten-year Allied occupation of Germany, would be quite a logical time for it to break surface in American English.