Hot Under The Collar Meaning

(idiomatic, of a person) Angry, agitated.

Example: 1914, Ralph Henry Barbour, Left End Edwards, ch. 21:
  "Oh, cut it," said Steve wearily. " . . . I don't want to listen to drivel like that."
  "Drivel?" repeated the other, puzzled. " . . . I don't see why you need to get so hot under the collar.
1919, P. G. Wodehouse. "Jeeves and the Hard Boiled Egg," in My Man Jeeves:
  "What do you mean, sir?" cried the old boy, getting purple. . . .
  "Now don't get hot under the collar. I'm only asking. I've a right to know."
1951, "Poor People! Seats In The End Zone," Kentucky New Era, 21 Dec., p. 9 (retrieved 30 Sep 2010):
  The Tennessee Football fans who couldn't buy Sugar Bowl tickets were furious, but it's a toss-up whether they were any hotter under the collar than some of those who got them.
2008, "IFP angry at 'history distortion'," Independent Online (South Africa), 14 May (retrieved 30 Sep 2010):
  A controversial history textbook has IFP members hot under the collar and has resulted in two protest marches being scheduled for KwaZulu-Natal on Wednesday.