The phrase "where does someone get off doing something?" expresses a sense of indignation or outrage, and there are several synonyms that convey similar sentiments. For example, one might ask "who do they think they are?" or "what gives them the right?" to suggest that the person in question has overstepped their bounds. Other options include "why are they so presumptuous?" or "how dare they act that way?" These phrases all convey a sense of disbelief or disapproval at someone's actions or behavior, and can be used to express frustration with individuals who seem to be acting unfairly or without regard for others.