'KUWTK': Khloe Kardashian Says She Wants to 'Slap' Sister Kourtney 'in the F**king Mouth' While in Bali

This family vacation started out rough and just got more angry as it went on in Sunday's new episode.

The sister drama is still going strong on Keeping Up With the Kardashians.

On Sunday's new episode -- which aired just days after Kourtney Kardashian celebrated her 40th birthday with her sisters by her side -- tensions were running high between Kourtney and Khloe Kardashian.

While on vacation in Bali, things weren't going smoothly between the sisters from the start. Khloe was tense, as this was the first time she was bringing along her infant daughter, True, on a family trip.

As it turns out, it was the flight to Bali that lead to the initial friction. Kourtney brought her kids along on the family getaway as well, but passed out for most of the insanely long flight, leaving Khloe to have to watch not only her own daughter, but play baby sitter to the other young children as well, for hours.

So, by the time everyone got to where they were going, Khloe was already fed up and it wasn't going to take much to send her over the edge. And, because KUWTK isn't anything without its blowups and sibling threats of violence, Kourtney managed to press the right buttons almost instantly.

After Kourtney spent quite some time complaining about how her assistant didn't pack her bags correctly, she then had the nerve to say "Khloe, I was just thinking, you complain a lot," and that she is "more chill" than Khloe.

This wasn't the right thing to say.

"Are you on crack? You're more chill?" Khloe said, getting heated, before turning to Kim Kardashian and Scott Disick. "Did you not hear her speech on the private plane? The bitch complains for hours!"

"Get out of my f**king business!” she added later, after Kourtney awkwardly laughed at her outburst. "I help you with your kids, I do this and that. I don’t have to do s**t. I don’t even have to f**king be here."

Speaking directly with the KUWTK cameras in a solo interview, Khloe continued to vent her anger, explaining, "Her comments make me want to slap her in the f**king mouth."

Tensions continued between the sisters throughout their trip, and seemed to cast a shadow over Khloe's entire time in the idyllic paradise.

Luckily, however, the pair agreed to take a scenic walk on the beach to talk about their combative relationship over recent days, and the cathartic conversation seemed to help them turn things around.

"I feel like we both get defensive,” Khloe said. “But I want to be able to communicate with you from a non-defensive place, where we could accept each other’s opinions."

Khloe also said that she feels Kourtney doesn't really pay attention to what she says or how it could impact other people. Kourtney agreed and promised to work on being "more present" when talking with her sister, while Khloe promised to work on not exploding in rage.

"I appreciate your helping raise everyone’s kids,” Kourtney finally offered as the two made up.

There didn't seem to be a hint of animosity between Khloe and Kourtney over the weekend during her lavish, personalized 40th birthday party, which featured a nude bathing lady cake and bottles of champagne with Kourtney's face engraved in them. Check out the video below for more on the over-the-top festivities.

Keeping Up with the Kardashians airs Sundays at 9 p.m. ET/PT on E!