Guns N' Roses perform at the DeLeon Tequila Rock Lounge at Hiro Ballroom in New York City. Credit: Getty ImagesTheo Wargo/Getty Images.

The last party of New York Fashion Week was, by far, the wildest. Guns N' Roses rocked Hiro Ballroom Thursday night, and on a balcony above the tequila-soaked fans, Matt Damon, Justin Timberlake and Chelsea Clinton got a little wild. Well, mostly Damon - while Clinton swayed to the music with her husband, Marc Mezvinsky, and a bearded, beanie-clad Timberlake chatted with friends (without fiance Jessica Biel), Damon "pounded beers all night," an onlooker told ABCNews.com.

"At the end of the night, around 2 a.m., he tried to climb over a couch to get to the bar and ended up falling on the floor," the source said. "He landed on his knees. But he was having a good time. He was making out with his wife all night."

Matt Damon. Credit: David Miller/ABC News.