To have a chip on one's shoulder refers to the act of holding a or grievance that readily provokes disputation. It can also mean a person thinking too much of oneself or feeling entitled.
History
This custom is known in North America since the early 19th century. The New York newspaper Long Island Telegraph reported on 20 May 1830 "when two churlish boys were determined to fight, a chip would be placed on the shoulder of one, and the other demanded to knock it off at his peril". A similar notion is mentioned in the issue of the Onondaga Standard of Syracuse, New York on 8 December 1830: "'He waylay me', said I, 'the mean sneaking fellow—I am only afraid that he will sue me for damages. 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'." Some time later in 1855, the phrase "chip on his shoulder" appeared in the Weekly Oregonian, stating "Leland, in his last issue, struts out with a chip on his shoulder, and dares Bush to knock it off". In American author Mark Twain's 1898 manuscript of Schoolhouse Hill, character Tom Sawyer states his knowledge of the phrase and custom when he says, "f you want your fuss, and can't wait till recess, which is regular, go at it right and fair; put a chip on your shoulder and dare him to knock it off." In Canada, the custom is well described at St. Peter Claver's Indian Residential School for Ojibway boys in the town of Spanish, Ontario: The challenger might further provoke his opponent by issuing a :wikt:dare|dare for him to knock off the chip. The opponent might then display his bravery and contempt by brushing the cheek of the challenger lightly as he did so. In more formal cases, a second might take the chip and present the chip to his man who would then place it on his own shoulder. The boys would then square off and fistfight like boxers.
In the 1970s a commercial for a household battery used Robert Conrad, who dared the viewer to knock an Eveready battery off his shoulder. The musical Legally Blonde has a song titled "Chip on My Shoulder". In this, after being accused of having a chip on his shoulder, Emmett Forrest explains to Elle Woods that the need to prove himself motivates him.
