We thought long and hard about this one – there are so many possible antagonists in this novel that it's hard to keep track. There's Fanny, Mrs. Ferrars, Lucy, Willoughby, and even his mysterious fiancée, Miss Grey…but none of them quite work as the villain here. No, instead we decided to take the abstract route, and pick on the force that drives all of those characters we just mentioned to their meanness: society.
It's social pressure that creates all of the problems we see – pressure to live up to one's social status, to exceed it, and to establish one's superiority over those of a lower rank. This pathological need to prove one's worth is emblematic of British society at the time, and Austen takes shot after shot at it, not just here, but in all of her books. It's social pressure (to be rich and important) that prevents Willoughby from marrying his true love, Marianne; it's social status that prevents Edward from getting a job, then from marrying first Elinor, then Lucy. Fortunately, the latter is able to break away from his family's expectations of his social goals, while sadly, that former can't abandon his social addiction.