The Collaborative International Dictionary of English v.0.48:

Insulting \In*sult"ing\, a.
   Containing, or characterized by, insult or abuse; tending to
   insult or affront; as, insulting language, treatment, etc. --
   In*sult"ing*ly, adv.

   Syn: Insolent; impertinent; saucy; rude; abusive;
        contemptuous. See Insolent.
        [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Insult \In*sult"\, v. t. [imp. & p. p. Insulted; p. pr. & vb.
   n. Insulting.] [F. insulter, L. insultare, freq. fr.
   insilire to leap into or upon; pref. in- in, on + salire to
   leap. See Salient.]
   [1913 Webster]
   1. To leap or trample upon; to make a sudden onset upon.
      [Obs.] --Shak.
      [1913 Webster]

   2. To treat with abuse, insolence, indignity, or contempt, by
      word or action; to abuse; as, to call a man a coward or a
      liar, or to sneer at him, is to insult him.
      [1913 Webster]

WordNet (r) 3.0 (2006):

insulting
    adj 1: expressing extreme contempt [syn: contemptuous,
           disdainful, insulting, scornful]

Moby Thesaurus II by Grady Ward, 1.0:

33 Moby Thesaurus words for "insulting":
   abusive, arrogant, atrocious, audacious, backhand, backhanded,
   bumptious, calumnious, cold, contumelious, cool, degrading,
   disdainful, familiar, forward, hubristic, humiliating, insolent,
   left-handed, obtrusive, offensive, outrageous, overpresumptuous,
   overweening, presuming, presumptuous, procacious, pushy, scurrile,
   scurrilous, unspeakable, uppish, uppity