I think in Mrs. Bennet's surprise, the information that for Elizabeth no meant no slipped out before second thoughts told her that it might be better to keep quiet for the time being!

I always laugh at Mr. Bennet's rejoinder too, but you have to admit that he is once again not only playing on his wife's nerves, but disrespecting her in front of one of her children. He might have expressed his refusal in so many different ways!