The Collaborative International Dictionary of English v.0.48:

Sorehead \Sore"head`\, n.
   One who is disgruntled by a failure in politics, or the like.
   [Slang, U.S.]
   [1913 Webster]

WordNet (r) 3.0 (2006):

sorehead
    n 1: someone who is peevish or disgruntled

Moby Thesaurus II by Grady Ward, 1.0:

35 Moby Thesaurus words for "sorehead":
   Tartar, bear, bellyacher, complainant, complainer, crab, crank,
   croaker, crosspatch, dragon, faultfinder, feist, fire-eater,
   frondeur, fury, griper, grizzly bear, grouch, grouser, growler,
   grumbler, hothead, hotspur, kicker, kvetch, malcontent, murmurer,
   mutterer, querulous person, reactionary, reactionist, rebel,
   sourpuss, ugly customer, whiner