Has anyone ever told you; "that guy has a chip on his shoulder"?
Surely you know that it means that guy is likely to be in a bad mood or ready to fight at the drop of a hat. Either way, you know to stay away from him. That's probably a good instinct.
The origins for the expression "a chip on your shoulder" actually comes from a time when guys (college aged- I'd assume) would put chips of wood on their shoulder and challenge each other to knock it off; which would end in a fight.
While you can no longer see the chip of wood, there are still many people walking around that you know is trying to bait you for a fight.
