Where can we find elements of comedy in Pride and Prejudice?

Certainly Mrs. Bennet is a source of humor for many. Her sheer ridiculousness and complete lack of self-awareness often renders her an object of horror for her two eldest daughters, but she is a font of hilarity for readers. The narrator describes her as having a mind not so "difficult to develope. She was a woman of mean understanding, little information, and uncertain temper. When she was discontented she fancied herself nervous. The business of her life was to get her daughters married; its solace was visiting and news" (Volume I, Chapter I). She is often oblivious to the social errors she commits, and even when she is not, she doesn't care enough to stop. Mrs. Bennet is basically an older version of Lydia, past the dangers associated with Lydia's age. She is vapid and silly.

Mr. Collins is yet another source of humor. He "was not a sensible man," though he had "a very good opinion of himself [....]  [H]is authority as a clergyman, and his rights as a rector, made him altogether a mixture of pride and obsequiousness, self-importance and humility" (Volume I, Chapter XV). His combination of proud haughtiness with his desire to flatter his social superiors, his high opinion of himself mixed with his ability to lower himself when called for in society makes him as ridiculous as Mrs. Bennet. He is constantly comparing everything to Rosings Park, his patroness's home, discussing the fixtures in that home along with their size, price, and so on. He is eager to make peace with the Bennets by choosing a daughter to marry, and when Mrs. Bennet informs him that Jane is taken, he quickly switches his affections to Elizabeth. His proposal to her is both insulting and absurd, and it is -- in large part -- hilarious and cringeworthy because he doesn't realize it.

Put the two together at the Netherfield ball, add Mary Bennet (with her eager desire to showcase her small talents) and Mr. Bennet (with his inability or unwillingness to abide by social convention), and we have the recipe for a horrifyingly hilarious scene. First, Mrs. Bennet speaks loudly about "her expectation that Jane would be soon married to Bingley" and how that "must throw [the other daughters] in the way of other rich men"  (Volume I, Chapter XVII). Then Mary leaps up "after very little entreaty" to play the piano for the company: "her voice was weak, and her manner affected. -- Elizabeth was in agonies." She sings a second song (which she ought not to have done), and Mr. Bennet jumps in and insists that she give "the other young ladies" an opportunity "to exhibit." His unfortunate word choice is likewise humiliating. Then, in the awkward silence which ensues, Mr. Collins stands up and begins an elaborate speech on the pleasures of music. "Many stared. -- Many smiled." This was neither the time nor the place for this conceited little man to wax philosophic about the subject of music; it was the time to actually have music. "To Elizabeth it appeared, that had her family made an agreement to expose themselves as much as they could during the evening, it would have been impossible for them to play their parts with more spirit, or finer success."

Through characters and scenes like this, we can find a great deal of humor. As Mr. Bennet says, "'For what do we live, but to make sport for our neighbours, and laugh at them in our turn?'"