Beauty is a pain!

On Sunday's episode of Keeping Up With the Kardashians, Kim Kardashian visits a plastic surgeon's office to get Botox injections -- and opts out of using the numbing cream!

"I think I can handle it," Kim, 29, tells the doctor. "I have a really high tolerance for pain."

But 26-year-old Khloe -- who Kim invited along for moral support -- is skeptical about her sister's desire to look younger.

"This is disgusting. I hate needles!" Khloe says. "You're so stupid."

Gripes Kim, "I don't even know why I brought Khloe along with me. I mean, she's just making all this noise and she's freaked out about the needles, and I just want her to shut up and just be supportive."

Does the younger Kardashian have a change of heart? Watch the clip (above) and find out!

The full episode of Keeping Up With the Kardashians airs Sunday, Sept. 12 at 10 p.m. (EST) on E!