An Etymological Dictionary of the German Language/Annotated/mutzen
mutzen, verb, ‘to dress up, adorn’; in the sense of ‘to be out of humour,’ from mucktzen, like Blitz from Blikz, schmatzen from schmackezen; but Modern High German aufmutzen, ‘to throw in one's teeth, blame,’ from Middle High German ûfmützen, ‘to dress up, adorn,’ Middle High German mutzen, mützen, ‘to dress, adorn.’ Aufmutzen thus means ‘to puff.’