Source : Webster's Revised Unabridged Dictionary (1913)

Disagreeableness \Dis`a*gree"a*ble*ness\, n.
   The state or quality of being; disagreeable; unpleasantness.

Source : WordNet®

disagreeableness
     n 1: the quality of being disagreeable and unpleasant [ant: {agreeableness}]
     2: an ill-tempered and offensive disposition [ant: {agreeableness}]