"Darcy smiled and said, "You are perfectly right. You have employed your time much better. No one admitted to the privilege of hearing you can think anything wanting. We neither of us perform to strangers." (Ch. 31)

I think Darcy’s comment “We neither of us perform to strangers” suggests that Darcy sees them sharing a trait but it is also the end of his excuses. He is admitting he did not trouble himself about the folks at the assembly (or anywhere) not because he is incapable but because he did not want to. The difference, as Darcy points out, is that Lizzy pleases people with her playing anyway while he did not and I suspect it is much to his chagrin after Lizzy sited his “arrogance, your conceit, and your selfish disdain of the feelings of others” as the foundation of her dislike of him and why she could never marry him. Perhaps until Lizzy rejected his proposal Darcy never had reason to concern himself with how strangers interpreted his taciturn, unsociable disposition. Thanks Connie! (;D)