the ultimate sacrifice- martyrdom
unadulterated- ripe for the adulterating. "Stomping through fresh, unadulterated snow"
unbeknownst- in dramatic irony
undead- deathly, but alive
underdog- someone everyone loves because no one else does
ungrammatical- spoken or written without any linguistic rules of conjugation, word order, or syntax (i.e. in a way that your English teacher doesn't like)
unPC- disliked by liberals because it opposes liberal ideas. Got 'em!
unsportsmanlike- not exhibiting the cheating, hypercompetitiveness, or general lack of integrity expected of athletes
upstate- heaven. "I know that you're sad about losing your dog, but remember we sent him to a nice farm upstate, where he can be happy and roam free."
urethral sounding- *screams*
utilize- (long) to use