1
general::
A belligerent attitude or grievance, as in Mary is easily offended; she always has a chip on her shoulder. This term actually was defined in a newspaper article (Long Island Telegraph, May 20, 1830): "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." [Early 1800s]
American Heritage Idioms