Why did Elizabeth turn down Mr Darcy's invitation to dance a reel?

Elizabeth believed that Darcy was making fun of her.

"Oh!" said she, "I heard you before, but I could not immediately determine what to say in reply. You wanted me, I know, to say 'Yes,' that you might have the pleasure of despising my taste; but I always delight in overthrowing those kind of schemes, and cheating a person of their premeditated contempt. I have, therefore, made up my mind to tell you, that I do not want to dance a reel at all—and now despise me if you dare."