TO HAVE A CHIP ON YOUR SHOULDER

The origin of this expression goes back to the 19th century, one way to chalenge someone to a fight was to place a wood chip on your shoulder and invite someone to knock it off at their own risk. It was a challenge as it was a knight throwing his gauntlet, if the opponent picked up the glove, or knocked the chip off your shoulder, the challenge was accepted and the fight was on.
Since then, someone who goes looking for a fight, and maintains a snotty and belligerent attitude, has a chip on his shoulder.