I'm a (something), not a (something else)

Used to emphasize one's status as a certain type of person to the exclusion of some other type. Modeled on the catch phrase of Dr. McCoy in the television series Star Trek, "I'm a doctor, not a (something)." A: "What do you think would be the best way to market our new app?" B: "Hey, don't ask me—I'm a programmer, not a salesperson." A: "Do you think you can repair the car?" B: "Lady, I'm a mechanic, not a miracle worker. This thing is totaled."