chip on one's shoulder

Meaning

Noun

• A form of challenge, in the same spirit as a medieval knight throwing down his gauntlet.
• A habitually combative attitude, usually because of a harboured grievance, sense of inferiority, or having something to prove.
• A tendency to take offence quickly.

Origin

• The saying originated during the 19th century in the United States, where people wanting a physical fight would carry a chip of wood on their shoulder, daring others to knock it off.