After some comments earlier in this group read about Jane Bennet's smiles, ("Miss Bennet he acknowledged to be pretty, but she smiled too much")I was surprised to find Darcy smiling a lot of time as well....
In Chapter 11
"And yours," he replied, with a smile, "is wilfully to misunderstand them."
In Chapter 18
"What think you of books?" said he, smiling.
Also in Chapter 18
"He smiled, and assured her that whatever she wished him to say should be said"
It seems like Jane Bennet isn't the only one to smile around people she like.....