See Julianne and Derek Hough Gross Each Other Out on 'Lip Sync Battle'

Little sister weirds brother out with the Lonely Island's 'I Just Had Sex'

Dancing With the Stars standouts Derek and Julianne Hough brought their sibling rivalry to the stage on Thursday's installment of Lip Sync Battle, showcasing their choreography chops while making each other deeply uncomfortable.

For the first round, Derek gave a spirited rendition of Macklemore and Ryan Lewis' "Can't Hold Us," making host L.L. Cool J. blush with the dancer's liberal seasoning of pelvic thrusts. Julianne in turn scandalized her brother with a sexed-up performance of "All About That Bass," but stacked the deck a bit by bringing out a special guest in the form of Meghan Trainor herself. "It was wildly inappropriate," Derek declared of the choreography.

Things got even more heated in the second round, which Derek led off with a comparatively classy performance of Sia's "Chandelier." Although he's hardly the first to don that trademark platinum wig to channel the Aussie singer, he put his own special spin on Maddie Ziegler's choreography. "Even if I don't win, he's never going to live this down," Julianne declared afterward. "That was the greatest thing I've ever seen."

If Julianne's dancing to Meghan Trainor's booty anthem upset her older brother, it was a minor blow compared to what came next. For her final act, she brought out two muscle-bound backup dancers to join her for the Lonely Island's "I Just Had Sex," grinding enthusiastically along while attesting to the good feelings in her penis. 

"I'm straight up traumatized right now," Derek said after the performance.

In the end, the gambit paid off and the little sister won that big shiny belt. "I'm very excited to show this thing off to my family, to Derek especially," Julianne said. 

Lip Sync Battle debuted on Spike at the beginning of April with a tense showdown between Jimmy Fallon and Dwayne "The Rock" Johnson. Other notable performances have included John Krasinski channeling Justin Timberlake on N'Sync's "Bye Bye Bye" and Anne Hathaway taking on Miley Cyrus' "Wrecking Ball."