On Tuesday's episode of The Hills, Kristin Cavallari rips into Stephanie Pratt for spreading rumors that she has been abusing cocaine.

"You love to run your mouth and make s--t up!" she tells Pratt, 24, who was arrested for a DUI last year and has battled drug problems.

Denying she spread any rumors, Pratt shoots back, "You have the bitchiest attitude! You can't even have a nice conversation ... You're just a mean person!"

Pratt demands an apology from Cavallari, 23, but she refuses to give her one.

"You're delusional," Pratt says as she storms off.