WordNet (r) 3.0 (2006):

undiplomatic
    adj 1: not skilled in dealing with others [ant: diplomatic,
           diplomatical]

Moby Thesaurus II by Grady Ward, 1.0:

35 Moby Thesaurus words for "undiplomatic":
   airy, brash, careless, casual, cursory, degage, disregardant,
   disregardful, easygoing, flippant, forgetful, free and easy,
   heedless, impolitic, inconsiderate, indifferent, insouciant, lazy,
   maladroit, oblivious, offhand, perfunctory, reckless, regardless,
   respectless, tactless, thoughtless, unheedful, unheeding,
   unmindful, unprepared, unready, unsolicitous, untactful,
   unthinking