]If Mrs. B's nerves have suffered from her husbands lack of compassion for over twenty years, why does she constantly set herself up to be the victim of his verbal barbs? The possibilities I can see are:

--She hasn't figured out (after two decades) not to say anything that will set herself up for one of hi set-downs,
--It's a desperate need for attention - any kind of attention,
--Depite her protests, she enjoys it.

IMHO, it's a combination of 1 and 2, but not 3. In chapter 1 we learn that "Mr. Bennet was so odd a mixture of quick parts, sarcastic humour, reserve, and caprice, that the experience of three and twenty years had been insufficient to make his wife understand his character". The paragraph goes on to describe the limits of Mrs. Bennet's intelligence, so I don't think she understands why he continues to put her down and, therefore, continues to be upset when he does.