OK, bragging rights goes to the best response here. I'm CP USAIr flyer, and time and time again have been placed in the position of being asked to change my "preferred" seat with a member of a family who wants to sit either next to their young child, debilitated spouse, newlywed... Really, it has all happened to me and I have yet to be prepared with a line that gets me out of the situation. It's very frustrating, especially considering the length to which I go to select/grab my seat (seatguru, early checkin, CP personal liaison...).

So, bragging rights and maybe even a moniker like "The Smith Response" goes to the person who comes up with the best line in response to this situation that gets you out of it without looking like a crud. Best I've come up witrh (but not used) is "Well, I had to pay extra to get this seat?"

This ought to be a good one!