Both of them are intolerable
At one point I felt bad for Oliver: he was willing to give her the cash equivalent of the entire house, pay alimony for the kids, i.e. give her everything she could ever want to start a new life: cash & freedom. I really didn't like Barbara being so selfish, although I can appreciate the fact she probably had tried in the past to make her own money and pay for things, but Oliver was probably too condescending then as well.
Still, I didn't feel that gave her the right to be a beggar and a chooser, especially when she was being offered such a great parting deal.
But then that dinner scene with Barbara's clients...Oliver just comes in and pisses on the fish? Barbara had never done anything like that to him even though he had been condescending to her during his business dinners. I mean here he was, confirming exactly what she was afraid of him doing, which is why she had put that false exterminator notice: that he was a selfish man who didn't have the natural capability of sacrificing himself for the happiness of others, even a little bit. She had never done anything to him like this, she had basic decency!
When people say this movie isn't representative of relationships they're either full of *beep* or happen to be in one of those rare storybook marriages. The people I know are always like this, petty and selfish until they realize it goes too far, then they kiss and make up until they start doing it all over again, to infinity and beyond.