Jane Austin's Pride and Prejudice shares a quality with Austen's other novel, Sense and Sensibility, in that the titles of each story represent the two strongest forces that drive the narrative, both manifested in the two main characters.
In this case, Pride would be Darcy. Darcy, himself, admits that he is quite proud of his family name, and that he sees nothing wrong in adopting a persona that shows how proud one is of the things one has achieved.
Unfortunately, Darcy's tendencies and behaviors make him look haughty and snobby rather than sincerely proud of himself. Yet, Darcy (as we see in the end) is not really as stuck-up as he acts: He simply has been raised with a clear understanding of his family legacy and the need to distance himself from people that are not his equals. This is a tendency more than a chosen behavior. The fact remains that Darcy is simply a proud man who, in time, learns to separate pride from snobbery.
On the other hand, Elizabeth does not see any of this. She also has a bad tendency and that is to take things at face value without analyzing any deeper. She immediately labels Darcy as a proud man in every bad connotation that the term implies. Not enough with that, she allows every information about Darcy that comes from someone as creepy as Wickham to influence her opinion of Darcy even more. In other words, Elizabeth is completely prejudiced against Darcy (and people like Darcy) from the very beginning.
Therefore, Darcy is Pride, while Elizabeth is Prejudice. Darcy earned Elizabeth's prejudice by acting haughtily, instead of proudly. He also may have been a bit too proud as a rule. Contrastigly, Elizabeth's prejudice was caused by Darcy and his friends.The "Bingley Set" (minus Mr. Bingley) did not help much in changing Elizabeth's perceptions of them. However, in the end, both Darcy and Elizabeth along with all the pride and the prejudice that prevails in the story, are able to find a happy medium.