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Nobody messes with Brody Jenner's little sister.

In a new clip that has surfaced online from the next episode of "Keeping Up With the Kardashians," Jenner, 30, and his younger half sister, Kendall, 18, are at a bar in Thailand on a recent family vacation. While Jenner orders a round of drinks, his sister stands nearby.

That's when a man sitting on a barstool reaches out to grope Kendall's bottom.

"Excuse me!" the up-and-coming model exclaims in the video, quickly moving to her brother's side.

"Brody, that guy just touched my a**," she tells him. "That guy just grabbed my a**."

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Her big brother reacts immediately, confronting the man.

"Did you just f***ing touch my sister?" he asks.

The guy denies it, but Brody is unwilling to let it go.

"Are you f***ing kidding me, bro?" he says, knocking the man's sunglasses off his head.

The full episode airs Sunday, Aug. 3.