Chip on Your Shoulder

Etymology:

• This term has been taken from a game that American boys used to the play in the 18th century. They used to place a chip of some wood on their shoulder and asked the opponent to hit it. If it was dropped both of them would fight. Now this idiom is used to describe a person, who likes to invite an argument or a fight for no obvious reason. This idiom represents the theme of that game in an accurate manner.