Kourtney breaks down in tears over Kim's treatment of her, before the fight goes to a new, nasty level.
After arguing over the family's Christmas photo shoot -- which ended with Kim saying her sister is the "least exciting" Kardashian to look at -- Kourt calls Khloe crying, not knowing she's on speakerphone as Kim listens.
"I'm not here to be f--king mistreated by my f--king bitch family," Kourtney says through tears over the phone. "Kim saying I'm the least interesting to look at, who even speaks like that?!"
"Khloe, you don't say things like that. You guys just have really different values to me," she continues. "I chose to be a mother to my three kids, I'm not here looking for another job. I already work enough."
As Kourtney speaks, you can see Kim just itching to explode. Khloe puts the phone on mute so Kourt can't hear Kim scream, "YOU DON'T F--KING DO S--T!" before Kim demands to let her speak to her sister. That's when Kim doubles down, telling Kourtney, "You don't do s--t ... be accomodating to the people that actually do s--t."
Momager Kris Jenner tries, in vain, to mediate, telling her daughter, "Don't be mean, Kim." That plea, however, goes unanswered.
"You're a very distraught, evil human being," Kourtney responds. "I don't want to see you, okay? I don't agree with who you are as a human being."
Though Kim apologizes for some of the things she said, Kourtney can hear the falseness of her words through the phone. "F--k you, Kim, you meant it," Kourtney shoots back. "I'm not going to live my life around people that make me feel not good on a daily basis."
That's when Kim calls her sister a "f--king lunatic" and "the most f--king entitled person on the planet, when you work the least."
Watch the explosion above. "Keeping Up with the Kardashians" premieres Sunday night at 9pm on E!