Didn't Karl Talk to Him About This?
He made a joke about scowling, so obviously Bush realizes he can't give any fodder to those who charge him with being "arrogant" or "petulant"—then he cuts of Charles Gibson. Good odds that ends up as one of the clips that get rerun on the weekend talking head shows.
Postscript: Yup, they're already rerunning that segment, though that alone probably won't hurt him much.