from The American Heritage® Dictionary of the English Language, 4th Edition
- adj. Chiefly British Ill-tempered; angry: "He saw how shirty she was about it” ( P.G. Wodehouse).
from Wiktionary, Creative Commons Attribution/Share-Alike License
- adj. ill-tempered or annoyed.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- adj. (British informal) ill-tempered or annoyed
Probably from to get someone's shirt out, to annoy.(American Heritage® Dictionary of the English Language, Fourth Edition)