Lizzy is surrounded by proud people whom she tolerates. Her mother expects to be the toast of Meryton society. Note the constant small-minded competition with Lady Lucas: whose daughter attracts Mr. Bingley's notice is not just an economic concern of Mrs. B but a bragging right as well. Mr. Bennet is too self-satisfied to attend the assembly with his family (perhaps only I think that odd). Lizzy puts up with the SS's pride, and likely could have suffered Darcy's as well if it were limited to general haughtiness and exclusivity.

But his remarks to Bingley about her at the assembly, after catching her eye and increasing the likelihood that she would overhear, were excessive and personal and (insofar as Darcy assumed she was neglected by other men) unfounded. To Lizzy, his treatment of her was mean, unworthy of a gentleman; and if she then reinterpreted his general haughtiness in light of this, it was a damning portrait indeed.