The Collaborative International Dictionary of English v.0.48:

Inconsideration \In`con*sid`er*a"tion\, n. [L. inconsideratio:
   cf. F. inconsid['e]ration.]
   Lack of due consideration; inattention to consequences;
   inconsiderateness.
   [1913 Webster]

         Blindness of mind, inconsideration, precipitation.
                                                  --Jer. Taylor.
   [1913 Webster]

         Not gross, willful, deliberate, crimes; but rather the
         effects of inconsideration.              --Sharp.
   [1913 Webster]

WordNet (r) 3.0 (2006):

inconsideration
    n 1: the quality of failing to be considerate of others [syn:
         inconsideration, inconsiderateness, thoughtlessness]
         [ant: considerateness, consideration, thoughtfulness]