The meaning of "have a chip on one’s shoulder" is:
The definition of "have a chip on one’s shoulder" is:
(idiom) when one has a very bad attitude because one feels wronged
A: What’s wrong with our teacher? Why is she so mad?
B: She has a chip on her shoulder because all of her students were late today.
I have a chip on my shoulder because my neighbours kept me awake all night with a loud party!