The "Late Late Show" host also visits Demi Lovato and Ed Sheeran backstage at the annual Los Angeles pop music spectacular.
James Corden took "Late Late Show" viewers behind the scenes of this year's iHeartRadio Jingle Ball concert, where he stepped in as general manager of The Forum to annoy -- errr -- check in on Taylor Swift, Ed Sheeran, Demi Lovato, Sam Smith, Niall Horan and Liam Payne before the show.
After stopping by each of the singers' dressing rooms, Corden received a call from Swift, who was in desperate need of a replacement backup dancer after one of hers bailed at the last minute.
Corden put his GM duties aside to step in for Swift.
"Taylor, I heard the news, I heard what's going down, you're a dancer down, how's it going, use me," a mesh-clad Corden said to Swift before the show.
He proceeded to make himself right at home with Swift and her on-stage squad, only to be ditched when they saw their opportunity for escape.
"Alright, guys -- I'm going to go to the bathroom," Corden said to the crew. "I'm going to get ready and we are going to give this a hell of a show."
As soon as he left, Swift looked at her dancers and said, "Save yourselves. Go now. Run. Run! Do not walk."
The hilarious video below is worth every minute of your time.