a chip on your shoulder

a chip on (one's) shoulder

An attitude that leads one to become combative or easily angered. Fred has such a chip on his shoulder—you never know what's going to set him off next. She won't admit it, but Kate has a chip on her shoulder when it comes to discussing her career.
See also: chip, on, shoulder
Farlex Dictionary of Idioms.

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’.
See also: chip, on, shoulder
Farlex Partner Idioms Dictionary
See also:
  • chip on one's shoulder
  • chip on shoulder
  • a chip on (one's) shoulder
  • have a chip on (one's) shoulder
  • have a chip on your shoulder
  • have a quick temper
  • quick temper
  • short temper
  • be on/have a short fuse
  • have a short fuse