have a chip on your shoulder

have a chip on (one's) shoulder

To have 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, have, on, shoulder
Farlex Dictionary of Idioms.

have a chip on your shoulder

COMMON If someone has a chip on their shoulder, they feel angry and resentful because they think that they have been treated unfairly, especially because of their background. She thinks he has a chip on his shoulder because he didn't go to university. Note: You can also use chip-on-shoulder or chip-on-the-shoulder before a noun. This sort of chip-on-the-shoulder nationalism makes neighbouring countries nervous. Note: There is a story that in America in the past, men sometimes balanced a small piece of wood on one shoulder in the hope that someone would knock it off and give them an excuse to start a fight.
See also: chip, have, on, shoulder
Collins COBUILD Idioms Dictionary, 3rd ed.

have a ˈchip on your shoulder

(informal) be sensitive about something that happened in the past and easily offended if it is mentioned, because you think you were treated unfairly: He’s got a chip on his shoulder about not having been to college.This idiom comes from a nineteenth-century US custom. If a boy wanted to fight, he put a small piece of wood on his shoulder. He would begin a fight with whoever knocked the chip of wood off his shoulder.
See also: chip, have, on, shoulder
Farlex Partner Idioms Dictionary
See also:
  • have a chip on (one's) shoulder
  • a chip on (one's) shoulder
  • a chip on your shoulder
  • chip on one's shoulder
  • chip on shoulder
  • have a quick temper
  • quick temper
  • short temper
  • have a short fuse
  • be on/have a short fuse