The whole deal in one dialogue exchange.
Best part of the movie imo is when Billy asks Myra why she married him. She says "Because you're weak. Because you needed me..." and he says "Well, those are two good reasons." In fact those were the reasons he has for being with her. This character interplay, the notion that she believes he is the dependent one when in fact he is her crutch really encapsulates the entire story in one exchange. It's a bit of genius.
"Do you realise that Otto spelled backwards is Otto?"