The friends and neighbors have a tradition of alternating pranks each year. But this year, "The Office" alum stole Kimmel's turn and surprised him with several gimmicks throughout the week.
"This is my greatest joy with the prank this year. That we alternate and I robbed you of the joy," Krasinski gloated on Kimmel's late-night show Tuesday. "And when I did the prank I remember seeing your eyes like, 'That's really funny! I hate you.'"
Kimmel then showed a video of how Krasinski managed to fool him. First, the actor hired a Santa Claus -- wearing a coat and not much else -- to scale Kimmel's office window. Then, he hid a live reindeer in his dressing room.
"That thing crapped all over my bathroom," Kimmel said.
But Krasinski didn't stop there. He decorated Kimmel's office to look like the North Pole, then surprised him dressed up as a giant nutcracker.
But that wasn't all. The host "nogg'd" his friend on the set Tuesday, covering the actor in eggnog as their prank war continues.
Check out the video below!