How about... with a smile - "I try to be, but there so many MORE people who are WAY more clever..."
I did actually try almost exactly those words once, but the other person didn't quite hear or didn't quite understand, and wanted the remark explained, which I found excruciating... I suppose my main issue with this is that I don't want to talk about the subject at all, and certainly don't see why I should do so with a random stranger who is just expressing a stereotype. Maybe I should just practice looking obviously embarrassed!
