A chip on your shoulder

Carrying a persistent grudge or sense of inferiority, often leading to defensiveness or a readiness to take offense at perceived slights. It paints a picture of someone burdened by a small but nagging resentment.

From 19th-century America, this phrase began as a literal challenge. Boys would place a wood chip on their shoulder, daring others to knock it off and start a fight-a test of honor in rough-and-tumble towns. The New York 'Long Island Telegraph' in 1855 noted it as a brawling custom, and by the 1880s, it morphed into a metaphor for emotional baggage. It reflects a frontier culture of macho pride and lingering scores, evolving into a psychological idiom as urban life softened the physical stakes.