He always walks around with a chip-on-the-shoulder attitude, believing everyone looks down on him.

chip-on-the-shoulder 是一个固定短语，字面意思是"肩膀上扛着木屑"，源自19世纪美国的一种挑衅行为：把木屑放在肩膀上挑战别人打掉它。现在用来形容"容易生气、总觉得被冒犯"的心理状态，带有"愤愤不平、好斗"的态度。