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
You cannot make order from chaos. Chaos is always chaotic. But you can take out and define subsets from the whole, things that make sense, and from each of those, begin to understand...