How does the title of Jane Austen's Pride and Prejudice relate to Darcy's proposal and Elizabeth's response?

The title of Jane Austen's Pride and Prejudice reflects the the dominant theme of pride found in Darcy's proposal speech to Elizabeth and the prejudice found in both her reply and in her overall judgement of his character.

As we learn in Darcy's letter to Elizabeth, Darcy had rightly judged the Bennet family to be beneath his own breeding and dignity. One reason why he feels the Bennet family is beneath him is because Mrs. Bennet comes from the working class, whereas Darcy has nobility in his family line. But, more importantly, he sees that the Bennet family members behave in ways that are beneath high social standing; they act with impropriety. Specifically, both Kitty and Lydia our outrageous flirts, and Mary tries to draw unwarranted attention to herself, as seen in her insistence on playing the piano at the Netherfield ball. In addition, their mother is a vain gossip, and, worse yet, their father does nothing to check the behavior of his family members. As a result of judging the Bennet family to be beneath him since he takes great pride in his own virtuous behavior, Darcy felt it necessary to express his own pride in his proposal speech to Elizabeth, as we see in Austen's following narration:

He spoke well; but there were feelings besides those of the heart to be detailed; and he was not more eloquent on the subject of tenderness than of pride. His sense of her inferiority--of its being a degradation--of the family obstacles which judgement had always opposed to inclination, were dwelt on with a warmth which seemed due to the consequence he was wounding, but was very unlikely to recommend his suit. (Ch. 34)

Though Darcy speaks truths, Elizabeth had already formed a prejudiced opinion of Darcy's character, and her prejudices blind her to the truth of what he is saying. Elizabeth formed a prejudiced opinion of him the moment he snubbed her and all company at the Meryton assembly. Her prejudiced opinion was further solidified when she chose to believed Mr. Wickham's version of why he and Darcy are no longer cordial and still further when she learned Darcy had discouraged Bingley from proposing to Jane. It's due to her prejudices that Elizabeth responds to his proposal by attacking his character. As the novel progresses and Darcy begins to show how genuinely caring his nature really is, Elizabeth realizes just how prejudicially she had judged Darcy.