Region: US | Usage example: He has a chip on his shoulder after being passed over for promotion.

Chip on your shoulder

Meaning

Carrying a grudge or feeling defensive about a perceived slight.

Used when describing someone quick to take offense.

Origin notes can vary by region and source; this page gives the commonly reported explanation and usage context.

19th-century boys would place a wood chip on their shoulders as a challenge to peers.

Moved into adult idiom to describe people looking for conflicts.