Man, he wasn't kidding.
In a move that provides quite the dilemma for Cleveland fans, James not only sported enemy gear to Thursday's Game 1 against the Yankees at Jacobs Field, but he even playfully taunted fans by doffing his Yankees cap and raising it in front of a camera during an interview with TBS.
James may be the city's biggest star who revived Cleveland basketball and brought the Cavaliers to the NBA Finals last season. But did he cross the line? Are some things best kept hidden?
"It's like [Indians ace] C.C. [Sabathia] walking out there with a Pistons hat," said Kevin Lowrie, 48, of Mentor. "Yeah, it's who he roots for, but does he have to brag about it like that? It's wrong."
"I think he should be traded for that," said 30-year-old Joe Dickinson, with a laugh. "Cheer in secret."
Even New York fans thought it was odd for the longtime Yankees fan to flaunt his team's colors in the town that idolizes him.
"I can't understand it," said Rob Fath, 19, of Yonkers, N.Y. "It's really pretty low of LeBron, to be honest. Why would he do that to his city?"
At least it offered the Yanks' faithful some needed humor -- and solace.
"That offers a lot of comfort," said Dave Molyneaux, a 42-year-old Yankees fan from Gainesville, Fla. "That's pretty stellar of him to wear that hat."
Yet in the end, the Indians and the sellout crowd of got the last laugh in a 12-3 victory. James eventually succumbed to the demands of nearby fans shouting for him to take off his hat. And as the Indians pulled away in the sixth inning, James summoned his entourage to the exits.
There is, of course, another side to this story. Some fans simply don't care.
"Who cares? I love LeBron. How can you not?" said 27-year-old Jason Maxey. "He can wear a Pittsburgh Steelers jersey for all I care. It has nothing to do with basketball."
"He can do whatever he wants. When he was young, the Tribe was bad, so what are you going to do?" said Derek Yurtz, 33, of Medina. "Whatever makes him happy. If rooting for the Yankees helps him shoot threes, he could vote for Satan."
Most fans, however, fell along the lines of Tribe Hall of Fame pitcher Bob Feller. Rooting for the Yankees? Fine. A Cleveland representative wearing Yankees gear? Not fine.
"I'm going to a Cavaliers game and sit right by their bench, wearing a Detroit Pistons cap. Let's see how LeBron likes that," Feller told the Cleveland Plain-Dealer.
"Really," said Dickinson, "it's ridiculous."
David Briggs is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.