I've been in a similar situation a couple of times before, and I always make a point to apologize directly to the child for their parent's 'terrible behavior'. That usually gets the shitty parent really riled up, which is always good for a laugh.
Madness string 98197
Look, if you're expecting me to apologize for damaging a family heirloom, let me just point out that you were trying to skewer me with it.