The Collaborative International Dictionary of English v.0.48:

Insufferable \In*suf"fer*a*ble\, a.
   1. Incapable of being suffered, borne, or endured;
      insupportable; unendurable; intolerable; as, insufferable
      heat, cold, or pain; insufferable wrongs. --Locke.
      [1913 Webster]

   2. Offensive beyond endurance; detestable.
      [1913 Webster]

            A multitude of scribblers who daily pester the world
            with their insufferable stuff.        --Dryden.
      [1913 Webster]

WordNet (r) 3.0 (2006):

insufferable
    adj 1: used of persons or their behavior; "impossible behavior";
           "insufferable insolence" [syn: impossible,
           insufferable, unacceptable, unsufferable]