Ashlee Simpson Gets Drunk, Gives Pete Wentz A Lap Dance, Everyone Throws Up

Ah, Jagermeister, the gift that keeps on giving, until you tell your husband’s ex-girlfriend that you were sleeping with him the entire time they were going out.  Yeah, that happened.

An out-of-control Simpson loudly trash-mouthed "Gossip Girl" actress Michelle Trachtenberg on Monday night at the "DJ Hero"; video game party at LA's Wiltern Theatre, according to PerezHilton.com.

PHOTOS: Celebs at DJ Hero Video Game Party

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."

Meanwhile, Wentz and Simpson will celebrate his 30th birthday this weekend at club Bank at the Bellagio.