WordNet (r) 3.0 (2006):

untactful
    adj 1: lacking or showing a lack of what is fitting and
           considerate in dealing with others; "in the circumstances
           it was tactless to ask her age" [syn: tactless,
           untactful] [ant: tactful]

Moby Thesaurus II by Grady Ward, 1.0:

58 Moby Thesaurus words for "untactful":
   airy, blanket, brash, careless, casual, cursory, degage,
   disregardant, disregardful, easygoing, flippant, forgetful,
   free and easy, general, heedless, impolitic, imprudent,
   inconsiderate, indifferent, indiscreet, indiscriminate,
   indiscriminative, insensitive, insouciant, lazy, maladroit,
   nonjudgmental, oblivious, offhand, perfunctory, promiscuous,
   reckless, regardless, respectless, tactless, thoughtless,
   uncritical, uncriticizing, undemanding, undifferentiating,
   undiplomatic, undiscreet, undiscriminating, undiscriminative,
   unexacting, unfastidious, unheedful, unheeding, unmeticulous,
   unmindful, unparticular, unprepared, unready, unselective,
   unsolicitous, unsubtle, unthinking, wholesale