Jimmy Fallon's Craziest "Tonight Show" Moments

Now, this is an unlikely trio!

Will Ferrell created some buzz on "The Tonight Show" when he stepped on the stage singing about his "tight pants," rocking some figure-hugging slacks, a short-sleeved green turtleneck and white boots. Then, the crowd went wild when his partner-in-crime, Christina Aguilera, popped up to join in.

The pop star was wearing her own version of tight pants, which featured a fold-over waistband with a colorful chevron topper.

"Everybody's talking about my tight pants, my tight pants," the unlikely duo sang. "I got my tight pants on!"

Host Jimmy Fallon joined in on the fun, but his guests were not pleased to see him. "Ever since we moved to this town, everybody we know has been talking about our tight pants," Ferrell said.

Things start to get heated when the actor had to defend Aguilera, who played his wife in the sketch. "You listen to me you fat face cobb knobler," Ferrell told Fallon. "I don't know who you are or what butt hole you crawled out of, but this is my woman."

Check out the hilarious clip below to see Will and Xtina force Jimmy off the stage!

Later in the show, Christina talked about the upcoming season of "The Voice."

The "Beautiful" singer admitted that she's hoping to break the "girl curse" and take home her first big win.

"This year, my team is really solid," she declared. "Even the boys are like, 'Man, you might break the girl curse this year.'"

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Xtina has another girl in her corner -- celebrity mentor Miley Cyrus.

"She's so much fun!" Aguilera said. "We're both fire signs, which I love. She likes to live in the moment and she's free. She won't let the boys push her around."

We'll have to wait and see if Xtina and Miley can bring one home for the ladies!