Afterall, he declined introductions at the Meryton Assembly, and didn't want to have anything to do with anyone outside his own company: "Mr. Darcy danced only once with Mrs. Hurst and once with Miss Bingley, declined being introduced to any other lady, and spent the rest of the evening in walking about the room, speaking occasionally to one of his own party." Ch. 3

In Ch. 5 Mrs Bennet says: "Mrs. Long told me last night that he sat close to her for half an hour without once opening his lips."

"Are you quite sure, ma'am? is not there a little mistake?" said Jane. "I certainly saw Mr. Darcy speaking to her."

"Ay -- because she asked him at last how he liked Netherfield, and he could not help answering her; -- but she said he seemed very angry at being spoke to."

"Miss Bingley told me," said Jane, "that he never speaks much, unless among his intimate acquaintance. With them he is remarkably agreeable."

To people outside his own circle, he has proven unsociable and taciturn - and now he is indignant that dancing excludes conversation?? Hmm... I guess this is what happens when you run into Elizabeth Bennet;-D She is at this point (Ch. 6) "far from suspecting that she was herself becoming an object of some interest in the eyes of his friend" (i.e. Mr Darcy) and that "He began to wish to know more of her, and as a step towards conversing with her himself, attended to her conversation with others."

But why that extra step? What is stopping him from simply talking to her? Surely he must know how to talk to women?