The goal of every medical school, residency, and fellowship interview is to distinguish yourself from everyone else to demonstrate you're worthy of a competitive spot. So what happens when you get this (ugly) question:
If there were one reason not to accept you, what would it be?When a (salty) faculty member asks you this interview question, her motivation might be to determine whether there's a weakness in your application she's missing. Or she may be assessing how you manage stressful situations by posing a question that is unpleasant.
While you need to be honest throughout the entire application process, you do not need to volunteer information that might harm you. So, for a charged question like this one that conflicts with your goal, you might answer, “While no candidacy is perfect, I have a strong application, and I don't see a reason not to accept me." Then you can leverage the question as an opportunity to mention the strengths of your candidacy. Remember: You have a duty to further your application, not damage it.
Contact me for mock interview help. I still have some October slots open, as of this writing.