My answer would depend upon the person asking the question. If I felt the person were fragile and insecure, I might answer, “You could be right, we’re all intelligent in different ways.” There’s no point in hurting someone who is lashing out because they feel inferior. In most cases, I would just smile, because time too precious to waste on such a silly assertion.
However, on the rare occasion that I might feel it was worth the time for putdown, I would say, “You could be right. How many times higher is your IQ than mine?” Since IQs of reasonably intelligent people fall between 100 and 190, it’s not possible for someone to have an IQ that is an integral multiple of another person’s IQ.
Once the person throws out a number like 2, 3 or 4, they are stuck. For if they say “3”, I would ask, “What is your IQ?” Of course they may throw out a number like 150, to which I might respond, “That makes my IQ 50. I should count myself lucky that I’m able to feed myself!”
By making a joke of the assertion, you deny the person making the statement, the joy of putting you on the defensive. Humor is the best antidote to a mean-spirited assertion.