Antonyms of sensitive:
insensible, insensitive, thick-skinned, tough-skinned, unaffected, unclassified, pachydermatous, indurate, dull, dead, numb, painless, unreactive, soulless, deadened, callous, big, clumsy, great, huge, large, stout, blunt, coarse, heavy, immense, rude, thick.
Examples of usage:
  1. How much more had he said to that sensitive nerve- drawn child of his?
    "Mary Wollaston", Henry Kitchell Webster.
  2. Mr. Kasson begged us to pretend not to notice it, because the man was very sensitive on the subject.
    "The Sunny Side of Diplomatic Life, 1875-1912", Lillie DeHegermann-Lindencrone.
  3. She's such a sensitive subject, that is the trouble.
    "Molly Brown's Junior Days", Nell Speed.