We find that Darcy is aware of Caroline's shallowness, and insecurity by the way he continuously deflects her attentions towards him and blatantly ignores her actions.
One scene that is particularly obvious is found when Elizabeth was staying at with the Bingleys during Jane's illness and Elizabethh went out to walk with Mrs Hurst, Miss Bingley and Darcy. When the ladies basically said that the road was too narrow for four people to walk together, Darcy sensed it and proposed to walk in the avenue. Elizabeth rejected and walked away happily.
In a second confrontation, Darcy finally throws the final blow at Miss Bingley when she mentions Elizabeth's looks in a final attempt to get him to say something bad about Elizabeth:
``I remember, when we first knew herin Hertfordshire, how amazed we all were to find that she was a reputed beauty; and I particularly recollect your saying one night, after they had been dining at Netherfield, "Shea beauty! -- I should as soon call her mother a wit." But afterwards she seemed to improve on you, and I believe you thought her rather pretty at one time.''
To which Darcy was already a bit done with Miss Bingley and he responded
``Yes,'' but that was only when I first knew her, for it is many months since I have considered her as one of the handsomest womenof my acquaintance.''
And to add to this, he walked away leaving her alone in anger, basically telling her with his actions that he is quite finished discussing the topic with her.