nitpicker

nitpicker
    n 1: someone who makes small and unjustified criticisms
    

33 Moby Thesaurus words for "nitpicker":
      belittler, captious critic, carper, caviler, censor, censurer,
      common scold, critic, criticizer, equivocator, faultfinder,
      frondeur, hairsplitter, hedger, momus, mystificator, mystifier,
      obscurantist, palterer, perfectionist, pettifogger,
      picayune critic, precisian, precisianist, prevaricator, pussyfoot,
      pussyfooter, quibbler, scold, shuffler, smellfungus, stickler,
      tergiversator