There are new reports that the night Ashlee Simpson got drunk and was “too thin,” she also had a showdown with Michelle Trachtenberg, Pete Wentz’s ex. Ashlee and Pete were seated near Michelle and her boyfriend, and the two couples had a nice conversation where Ashlee even showed Michelle pictures of her son Bronx. But when Ashlee got drunker, it turned into a not-so-nice, one-sided screaming match. Ashlee started grinding up on Pete and giving him a lapdance while screaming insults at Michelle and telling her that the whole time Michelle was dating Pete, Ashlee was boinking him.

Ashlee, Jessica Simpson’s younger sister, had to be restrained at the event where Jay-Z and Eminem performed. The trouble started when Wentz and Simpson were seated near Trachtenberg, who dated Wentz before Simpson met the Fall Out Boy bassist.

According to PerezHilton: “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 [Trachtenberg] some baby pictures of [Ashlee’s] little boy, Bronx.”

But then Simpson started drinking. “Things got out of control,” an insider was quoted. An increasingly loud Simpson began to give Wentz a lap dance while staring directly at Michelle and hurling insults at her. “She was grinding up on Pete like a stripper. It was actually pretty disgusting,” a witness told the Web site.

Things reached a climax when Simpson screamed at a confused Trachtenberg, “I hope you know, the whole time you were dating Pete, I was [bleep]ing him!”

A bystander dragged Simpson away from Trachtenberg, who once starred in “Buffy the Vampire Slayer,” while Wentz looked mortified.

Trachtenberg’s spokesperson didn’t return Page Six’s calls. But Simpson’s rep said, “It was just a misunderstanding. Ashlee has since apologized to Michelle and they remain on good terms.”

[from New York Post]

We’ve heard in the past that there was some tension between Michelle and Ashlee. After Ashlee and Pete’s wedding, Michelle was talking sh*t about the couple in an airport and was overheard by one of Pete’s friends. The two clearly have some issues with each other, though I’m sure Pete loves being fought over.

It’s just low-class to yell in a crowded party about how you helped your husband cheat on his ex. But since their conversation turned from “look at pictures of my infant son” to insults, you have to wonder if Michelle said something first.

Here’s Michelle out shopping in Beverley Hills on the day of the altercation . Here’s Ashlee eating dinner with a friend at Il Sole yesterday. Images thanks to Fame Pictures .