Charles Barkley was confused after seeing Julius Randle give a thumbs-down gesture to Knicks fans during Thursday’s win against the Celtics.

“I never understand why players think you’re supposed get cheered when you’re playing bad,” Barkley said while discussing the Randle’s “thumbs down” he gave to fans in the fourth quarter of the 108-105 win at Madison Square Garden.

“No, you’re going to get booed when you’re playing bad and you’re going to get cheered when you win,” Barkley said, before hashing up the Javier Baez situation when the Mets star gave a thumbs-down to fans during the team’s rough stretch in August.

“This is the way this thing works. We ain’t doctors, we ain’t lawyers. If you play good, people cheer you. If you play bad, people boo you. That’s the deal you make with fans,” Barkley said.

Knicks fans started booing Randle on his home court after a slow start in Thursday’s game against Boston. With less than five minutes left in the fourth quarter, Randle scored a tough basket and gave a “thumbs down” gesture to the fans while running back on defense.

After the game, when asked what the gesture was for, Randle said, “To shut the f–k up.”

The day prior, Randle said he “doesn’t give a f–k what anybody has to say, to be honest,” while discussing recent criticism from fans and media.

On Thursday, Shaquille O’Neal gave Randle some tough love, like he has since the Knicks star became the face of the franchise.

“In a city like New York, if you’re the man on the team, gotta expect it. Heavy is the head that wears the crown,” O’Neal said. “You’re the man. I expect you to play good every night.”

Ernie Johnson noted that Randle could “do no wrong” during his All-Star year last season, when he led the turnaround in New York and helped push the Knicks to the playoffs for the first time since 2012-13. The power forward was rewarded with a $117 million extension this offseason.

Kenny Smith led the conversation off and said Randle “shouldn’t engage with fans” because “he’s too good a player.”

Randle finished with 22 points and eight rebounds on 8-of-20 shooting.

He’ll need to channel last year’s surge if the Knicks want to make a postseason run. Right now, they’re fighting for a spot in the play-in tournament, sitting in the tenth spot in the Eastern Conference.

The Knicks play the Celtics again Saturday in Boston.