a chip on your shoulder a strong and usually long-standing inclination to feel resentful or aggrieved, often about a particular thing; a sense of inferiority characterized by a quickness to take offence. informal

☞ In 1830 the Long Island Telegraph described the practice which gave rise to this expression: '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'.