So it's comforting to be able to tell you that the "mox nix" you heard growing up was not one of the seven warning signs of familial derangement. What you were hearing, in fact, was simply an English slang version of the perfectly proper German idiom "machts nichts," which means "It makes no difference."
Couldn't figure it out until I used my forgetten Deutsch
Das ist recht meine grosse Scwein.