Caroline Bingley does many things to suffer Austen's displeasure: it is clear that she is a proud and conceited individual, and Austen's authorial intrusion makes these negative characteristics clear. Certainly what spurs Caroline on is the competition she has with Elizabeth Bennet for Darcy's affections, and it is this that results in some of her more pointed barbs. However, one action that clearly draws the contempt of both the author and of Elizabeth is when she visits Jane when she is in London after Bingley has quit Netherfield. Note how Jane describes this meeting in a letter to Lizzie:
When she did come, it was vvery evident that she had no pleasure in it; she made a slight, formal, apology, for not calling before, said not a word of wishing to see me again, and was in every respect so altered a creature, that when she went away, I was perfectly resolved to continue the acquaintance no longer.
Although Lizzie has suspected all along that Caroline's partiality towards Jane was not sincere, it is clear through her actions in visiting Jane that Caroline Bingley is snubbing Jane, a woman that she formerly called a friend, because of the threat of her affections towards Bingley. To Caroline, her brother's marriage to a family such as the Bennets would be a disgrace, and this above all else singles her out for the author's displeasure. As Jane's account of her visit makes clear, Caroline puts social decorum and standing above friendship and affection, and it is this that makes her a bad character.