If you must deny Kristin Scott Thomas’s request, tell her no directly. Even offering no response at all trumps saying yes and then acting as if you hadn't.
Should Kristin Scott Thomas arrive unaccompanied at your restaurant, you would be wise not to greet her with “Just one?”
What you gain in efficiency by not replacing Kristin Scott Thomas's silverware between courses is not worth the lost diginity.
You shall remove your earbuds when engaging with Kristin Scott Thomas.
Were Kristin Scott Thomas to drop change on the sidewalk, you need not feel compelled to return it to her. Doing so simply forces her to act pleased about something that, rather literally, she could not give a sou about.
A Kristin Scott Thomas sigh is occasionally a sign of weariness. More often than not, however, it's from disappointment.