Girl Fight! Ashlee Simpson-Wentz Takes On Michelle Trachtenberg

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This is fabulous.

Pete Wentz had to play referee for wife Ashlee Simpson-Wentz and former girlfriend Michelle Trachtenberg, after Ash got a bit tipsy and, um, went nuts.

It all started out fine when the couple met up with Michelle at the "DJ Hero" video game party at LA's Wiltern Theatre. According to PerezHilton.com, "The evening started off very civilly. Pete and Ashlee had a pleasant conversation with Michelle and her boyfriend for close to 20 minutes, and even showed [Michelle] some baby pictures of [Ashlee's] little boy, Bronx."

But then Ashlee started throwing back drinks -- and things got messy.

"Things got out of control," an insider said. Ashlee began to give her hubby a lap dance, while staring at his ex and making inappropriate remarks to the Gossip Girl actress. "She was grinding up on Pete like a stripper. It was actually pretty disgusting," the witness blabbed.

Then Ash did the unthinkable -- she turned to Michelle, who was confused by the whole thing, and said, "I hope you know, the whole time you were dating Pete, I was [bleep]ing him!"

Oh no she didn't!

Pete reportedly was about to die when someone came and made Ashlee leave.

A rep for Ashlee said, "It was just a misunderstanding. Ashlee has since apologized to Michelle and they remain on good terms."

Riiight. Good terms, my hiney. Love it.