The Bennets's marriage is largely one of convenience. Like so many people of their time and class, they've been brought together for reasons which have absolutely nothing whatsoever to do with love or romance. They first became manacled together all those years ago because each had something the other needed. Mrs. Bennet brought money to the marriage, whereas Mr. Bennet brought social respectability.
Even though it was blindingly obvious to anyone with a functioning brain or eyes that the two were completely incompatible, they went ahead with their nuptials anyway and have been lumbered ever since with a marriage that is singularly devoid of mutual love or respect.
The difference in temperament between the Bennets is the most notable of the many that disfigure their marriage. Whereas Mr. Bennet is possessed of a sly, sardonic wit, Mrs. Bennet is a vulgar, humorless ignoramus whose stupidity is matched only by her emotional instability. Nevertheless, one could argue in defense of Mrs. Bennet that she's much more solicitous of her daughters' well-being than her laid-back—not to say, lazy—husband, whose hands-off approach leads to all kinds of problems, such as the flighty Lydia's elopement with the slimy Mr. Wickham.
It is Mrs. Bennet, perhaps over-compensating for her irredeemable vulgarity, who shows herself forever anxious to maintain her family's good name. Mr. Bennet, on the other hand, seems to find the various conventions concerning the so-called marriage market faintly absurd, which though a wholly admirable attitude in some respects, drives a further wedge between himself and his wife.