Re: Working with an Exec Question
You say, "F-you. What have you written?" Then storm out...
Or if you want to maintain the relationship...
Try and spin it: "Hey, you know what. That's a great observation. What I need to do is take some time to think about that and find a way to work it in with .... blah blah blah... (depending on the question) what I was trying to accomplish with the character/plot/theme, etc..."
Don't necessarily be afraid to straight out say it's something you hadn't thought about before -- make the producer feel like they are positively contributing to the script by bringing up something you might have missed -- but you think will make the script better if you work on it.