who does somebody think they are?
Who does (someone) think (they) are?
Why does someone think they have the right or the authority to behave in such a rude, arrogant, judgmental, or self-centered way? I work every day from dawn until dusk to provide for this family, and you accuse me of being lazy? Just who do you think you are? Who does he think he is, belittling me like that in front of the entire staff?