Jennifer Lawrence and Amy Schumer let their doofus flags fly while dancing on Billy Joel’s piano

Jennifer Lawrence and Amy Schumer are definitely in the honeymoon phase of their BFF-ness: On Thursday, they danced on Billy Joel’s piano while he sang “Uptown Girl.”

At Wrigley Field.

The two shrinking violets overcame their trademark shyness (We kid! We kid!) and put on a show for the stadium-size crowd, shaking it to a tune that was featured prominently in Schumer’s recent comedy, “Trainwreck.”

On Friday, the comic posted a video snippet of their antics on Instagram — just like she did back in July, when she made tons of people jealous showing herself, a bunch of her high school friends and Lawrence having more fun than everyone else in the world on a Hamptons vacation involving Jet-Skiing and human pyramid-ing.

“I was like, ‘Oh, we’re going on a boat tomorrow. You should come.’ It was kind of a hypothetical,” Schumer told Jon Stewart, explaining how they wound up together on that trip. “And she was like, ‘I think I’m coming.’ And I was like, ‘Oh my God!’ ”

A couple of days ago, Lawrence told the New York Times that she and Schumer were working on a screenplay together and intended to costar in it as sisters, and gave a heads-up that she was on her way to Chicago for a visit with her writing partner.

“I emailed her after I saw ‘Trainwreck’ and said, ‘I don’t know where to get started. I guess I should just say it: I’m in love with you,’ ” the “Hunger Games” star told the paper, explaining how they connected. “We started emailing, and then emailing turned to texting.”

Next thing ya know, you’re partying on Billy Joel’s piano.

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