Darcy, on the contrary, had seen a collection of people in whom there was little beauty and no fashion, for none of whom he had felt the smallest interest, and from none received either attention or pleasure. (Chapter 4)

Bingley would not knowingly conduct conservation such as their exchange about Lizzy at the assembly and he does not do that, his friend Darcy does. Despite Darcy’s past social offenses to which Bingley was assuredly a witness (Chapter 4), I am positive Bingley had no idea Darcy would specifically make disparaging comments about a particular lady’s appearance and unconfirmed accusations about her consequence in a room full of people with the lady sitting just behind him after ensuring he had her attention by meeting her eye. I am not saying Darcy intended to catch Lizzy’s eye but after doing so only a dunce would think he had not drawn the lady’s attention and she might overhear your conservation. I am not however advancing the theory Darcy is a dunce, I agree with the others who said Darcy just did not care if he was overhead by Lizzy or anyone else for that matter which is not the attitude or behavior of a gentleman. ;D