Patient's wife: We're worried he might have a brain injury from falling off the ladder
Me: Well, the CT scan didn't show anything but just to make sure, we'll do a cognitive screen on him
Patient's wife: What if he has a brain injury that's so severe that he can't work again?
Me: Sir, what is the derivative of 3x squared?
Me: I think he'll be OK.
For the record, I was the only person in the room who knew he was right. Thank you, premed calculus requirement. You finally came in handy for something.
(Fizzy says: You should have asked the integral of 6x and dinged him if he left off the constant.)