I had to look up the meaning....
http://www.urbandictionary.com/define.php?term=Chip on his Shoulder
This has gotten
lost in all the false meanings. A
chip on his shoulder comes from the days when there was a formal declaration for a fight, punch-up etc. When a
person disagreed strongly with someone over a personal belief, they would place a chip of
wood on their shoulder and
dare the other to knock it off. Once the other person did this signaled the beginning of the fight and thus punches were thrown. Examples of this can be seen in old
British movies circa 1930-1950's.
I've spent more time on this than I need to.