I’ve been waiting for any behind-the-scenes news about any kind of drama going down at Monday’s Costume Institute Met Gala, but I wasn’t expecting this – apparently, Lady Gaga was the night’s big diva. Gaga didn’t walk the red carpet, so we don’t have access to any photos of her costume – but you can see photos of her at HuffPo. It looks like a fancier version of the catsuit Jennifer Lopez wore for New Year’s. Anyway, Gaga didn’t walk the red carpet, and when she arrived, she ran to her dressing room and wouldn’t come out until Oprah “coaxed” her out. What gives, Gah?

Lady Gaga’s penchant for bizarre behavior continued at Monday’s Costume Institute Gala at the Metropolitan Museum of Art. Gaga was the slated performer at Vogue editor Anna Wintour’s annual fete, co-hosted this year by Oprah Winfrey and Gap creative director Patrick Robinson, though she refused to walk the red carpet and remained locked inside her dressing room for most of the evening.

“She literally wouldn’t come out,” says a spy. “Friends tried, [Warner Music exec] Lyor Cohen tried, no dice. Eventually, Vito Schnabel came over and got [artist] Terence Koh on the phone to talk to her, which helped. Koh and Oprah were the ones who finally coaxed her out.”

Once on stage, Gaga told the 700 assembled guests — including Anne Hathaway, Jessica Biel, Taylor Swift, Jennifer Lopez, Diane von Furstenberg, Barry Diller and Mayor Bloomberg — how she got the gig.

“I’ll never forget when Anna Wintour called me to play at this event, she called me and said, ‘I would like you to play at the Met gala, but I just want to make sure, because I’ve seen you perform before, that you won’t be swearing during the performance,’ ” Gaga explained. “So Anna, I will do my [bleep]-ing best!”

Most of the crowd seemed to enjoy the performance, except Bono — who left half-way through.

Later, at an after-party at the Mark Hotel, Pharrell Williams, Sean Combs, Usher and Justin Timberlake ended up having an impromptu jam session with DJ Cassidy.

“Pharrell first jumped in and started singing ‘Beautiful,’ and then Puffy jumped up and started rapping to ‘All About the Benjamins.’ He even grabbed Anna Wintour into the deejay booth. Finally, Usher and Justin joined in.”

Jude Law, Sienna Miller and January Jones were among those at the Mark, but it was Katy Perry who attracted the most attention. “She was out of control,” says a spy. “She was wearing a dress that had LED lights, and the switch was near her boobs. She was literally having people grope her to turn the dress on.”

[From Page Six]

Ooohhh… I wonder if Bono and Gaga are mortal enemies? They seem unlikely foes, but you can never tell with the two of them. That’s also interesting about Katy Perry. She wasn’t my choice for biggest disaster, but I’ll take it. My picks were Kate Hudson and Jessica Biel, just for the possible catfight they would have had over Justin Timberlake.