Green’s Dictionary of Slang

(US) coarse, boorish.

2003		W. Safire in Taipei Times 5 Oct. 9: zhlubby is synonymous with the British naff, ‘unfashionable, tasteless.’.
2004		Jewish Journal (LA) 🌐 David Krumholtz has a theory about why he’s played so many charming but zhlubby Jewish guys in film and on television. ‘I must be a zhlub myself.’.