As Lizzy reminds him during their conversation around the piano at Rosings in Chapter 31:

"Pray let me hear what you have to accuse him of," cried Colonel Fitzwilliam. "I should like to know how he behaves among strangers."

"You shall hear then -- but prepare yourself for something very dreadful. The first time of my ever seeing him in Hertfordshire, you must know, was at a ball -- and at this ball, what do you think he did? He danced only four dances! I am sorry to pain you -- but so it was. He danced only four dances, though gentlemen were scarce; and, to my certain knowledge, more than one young lady was sitting down in want of a partner. Mr. Darcy, you cannot deny the fact."

"I had not at that time the honour of knowing any lady in the assembly beyond my own party."

"True; and nobody can ever be introduced in a ball room. Well, Colonel Fitzwilliam, what do I play next? My fingers wait your orders."

"Perhaps," said Darcy, "I should have judged better had I sought an introduction; but I am ill qualified to recommend myself to strangers."