Definition: Holding a grudge usually over something in the past.
Origins: The American origin is not too far from the phrase’s definition. In the early 19th century, if someone was looking to fight, they would literally put a wood chip on their shoulder. They would then walk around with the “chip on their shoulder.” If someone wanted to accept the challenge they would knock it off.
The Long Island Telegraph printed the following in 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.
While the phrase “chip on his shoulder” appears around 1855 in the Weekly Oregonian:
Leland, in his last issue, struts out with a chip on his shoulder, and dares Bush to knock it off.
However, in England this phrase has a different origins story. At the Royal Navy Dockyards, around the 18th century, it was customary for ship carpenters to take home a certain amount of timber offcuts. By the 1750’s, they were thought to have abused that right. A new rule was instituted that the offcuts had to be what one could carry under their arms instead of over their shoulders.