Lose One's Rag Meaning

(idiomatic) To become angry.

Example: 1928, Ethel May Dell, The Gate Marked "Private", G. P. Putnam's Sons, page 248,
  […] he could not have said wherefore. “She was dressed as a bride if you must know,” he said. “But I don’t know what you’ve got to lose your rag about. She’s nothing to you.”
c1934, in Famous Plays of 1933–1934, page 449,
  Doll: Well, I’ll be trotting along. Sorry I lost my rag with […]
1937, Arthur Calder-Marshall, Pie in the Sky, C. Scribner’s sons, page 315,
  […] home now and was I going to come with him or wasn’t I? And I lost my rag and said, no, it was his duty to take me home, not mine to take him.
1944, in William Boyd (Ed.), Evacuation in Scotland: A Record of Events and Experiments, University of London Press, Ltd., page 187,
  There is frankness of discussion and remark. For instance, it is quite usual for a visiting member of the staff to ask, ‘How is your temper these days?’ The reply might be, ‘I haven’t lost my rag for a week,’ which is an achievement.
2006, Louise Rennison, Startled by His Furry Shorts, HarperCollins, ISBN 0060853840, page 127–128,
  The last time I went to God’s house, Call-Me-Arnold lost his rag with me. Which is a bit un-Christian. After all, there was no real damage done vis-à-vis the elderly pensioner’s scarf inferno incident.
2007, Patricia Ferguson, Peripheral Vision, Solidus, ISBN 1904529291, page 295,
  â€˜Come on, everyone loses their rag occasionally. It can’t be that bad. […]’