While dancing with Darcy at Netherfield, Lizzy says (among other things):

We are each of an unsocial, taciturn disposition, unwilling to speak, unless we expect to say something that will amaze the whole room, and be handed down to posterity with the eclat of a proverb.

To which Darcy replies:

This is no very striking resemblance of your own character, I am sure, said he. How near it may be to mine, I cannot pretend to say. You think it a faithful portrait, undoubtedly.

I have always taken this at face value: Lizzy saying they are alike in this way and Darcy saying she is not as she describes and being noncommittal as to whether or not it accurately describes him.

Well, I've been reading along with the group read, but only yesterday had a chance to catch up with the group watch of P&P2, and in the film, Darcy only says the first part of what's written (through "...I am sure.") and he says it very sarcastically!