Being able to understand Lizzie's words to Mr. William Collins are much easier to comprehend in knowing the true character of Elizabeth Bennett in Austen's Pride and Prejudice.
Lizzie is a strong-willed young woman, with equally strong opinions. For someone of higher station than Lizzy's struggling family, Lady Catherine de Bourgh would see these strengths as unflattering and undesirable in general—particularly for Collins, a clergyman looking for an appropriate wife. He needs a woman of service not given to strong—or even verbal—opinions. Lizzy is by no means the right woman for him, and she tries desperately to spare both of them an awkward proposal and refusal.
Collins believes women will initially turn down a man who intends to court her—to make him want her all the more. If there is a comical note here, it is based found in the fact that Lizzy cannot persuade him that she is indeed being truthful when she notes that she is not interested in his suit under any circumstances. Collins presents excellent arguments as to why a woman in Lizzy's circumstances would find his suit extremely advantageous. He wants to set an example for his parish by modeling the practice of marriage; he has been told by Lady Catherine that he needs to have a wife to improve his circumstances as a servant of the clergy; and (quite thoughtfully, in truth) that if they are married and her father dies, she can remain in the house, and the house will (in a way) "stay in the family."
When Lizzy graciously thanks him but refuses, he explains:
I am not now to learn...that it is usual with young ladies to reject the addresses of the man whom they secretly mean to accept, when he first applies for their favour; and that sometimes the refusal is repeated a second or even a third time. I am therefore by no means discouraged by what you have just said, and shall hope to lead you to the altar ere long.
Collins still believes Lizzy is "playing hard to get."
Lizzy tries in earnest to convince Collins that she is not such a woman. She would be more flattered if he would take her seriously, for this is central to Lizzy's nature. She is not a vapid female, waiting to be joined in marriage and give away her freedom so easily. She is a woman of sharp intelligence who sees a more non-traditional path for her, though she is not yet certain from where that path may originate. It certainly is not to be found as a wife to a clergyman in a country parish.
Lizzy assures Collins that she is not one of the ladies...
...who are so daring as to risk their happiness on the chance of being asked a second time.
She asks him to allow her to judge what is best for her—and ultimately, him. This would be praise indeed. Still Collins is having none of it. He does not credit Lizzy with enough intelligence to mean what she says—how could a proper young woman refuse him?
At length Lizzy responds...
I do assure you, Sir, that I have no pretension whatever to that kind of elegance which consists in tormenting a respectable man. I would rather be paid the compliment of being believed sincere. I thank you again and again for the honour you have done me in your proposals, but to accept them is absolutely impossible.
While some women in "elegant circles" may play with the feelings and pride of "respectable men," Lizzy is not one of them. Her use of the word "torment" shows her disregard for such behavior. She is very honest. Collins just doesn't believe her.