Derek Hough literally can't even with his sister Julianne Hough right now.

Julianne took home the coveted belt on last night's "Lip Sync Battle" -- and she made Derek super uncomfortable in doing so. Her winning performance of The Lonely Island's "I Just Had Sex" hit all the rights notes, but it might have been a little too risqué for her big brother.

Derek spent most of Julianne's one of a kind performance covering his eyes and ducking his head, and we can't say we blame him. It must be hard to watch your little sis grinding against two shirtless dudes. That being said, it was also H-O-T.

Of course, the five-time Mirror Ball champ on "Dancing With the Stars" didn't go down without a serious fight. Not only did he showcase some of his show-stopping tricks -- backflips! -- but he also donned Sia's famous wig for a hilariously quirky performance of the singer's hit "Chandelier."

Perhaps Derek would have secured a win if he would have fully committed to the part. (Yes, we're referring to stripping down into a nude leotard and baring his soul à la Maddie Ziegler.)

Better luck next time, Derek!