Chip On One's Shoulder Meaning

Example : A form of challenge, in the same spirit as a medieval knight throwing down his gauntlet.1830, The Onondaga Standard, Syracuse NY, 8 December:  â€˜Oh! if I only could get him to knock a chip off my shoulder, and so get round the law, I would give him one of the soundest thrashings he ever had.’1855, The Weekly Oregonian:  Leland, in his last issue, struts out with a chip on his shoulder, and dares Bush to knock it off.1906, Harold MacGrath, Half A Rogue, ch. 4:  The city of Herculaneum . . . held its neighbors in hearty contempt, like the youth who has suddenly found his man's strength, and parades round with a chip on his shoulder.2008, James Carney and Michael Grunwald, "Understanding John McCain," Time, 28 Aug.:  The young John McCain was a constant breaker of rules, a brawler and a slob, an undersize punk with an oversize chip on his shoulder.2014 November 17, Roger Cohen, “The horror! The horror! The trauma of ISIS [print version: International New York Times, 18 November 2014, p. 9]”[1], The New York Times:  [O]ne minute this "Jihadi John" was struggling to get by, and get accepted, in drizzly England, unemployed with a mortgage to pay and a chip on his shoulder, and the next he stands in brilliant Levantine sunlight, where everything is clear and etched, at the vanguard of some Sunni Risorgimento intent on subjecting the world to its murderous brand of Wahhabi Islam.