JUSTIN TIMBERLAKE: "I'M NOT TRYING TO BECOME A SERIOUS ACTOR YOU F---ERS"

Justin Timberlake put on a free concert with FreeSol at Irving Plaza in NYC for 901 Tequila on September 1 - and he had a message for all of the critics:

"For the record I'm not trying to become a serious actor you f---ers."

"The Social Network" star -- casual in jeans and a cream & black shirt -- came right out with the group FreeSol, an eyewitness tells Life & Style. "He began playing the keyboard as if he was just part of their band," the eyewitness says. "He was dancing and singing some backup and he knew all the words to their songs, but purposefully stayed in the background and let Freesol have the spotlight."

"And at one point during the set he sat on the floor behind his keyboard and chugged a beer," the eyewitness tells Life & Style.

Justin, who recently starred in "Friends With Benefits" and "Bad Teacher," then screamed out: "I wanted to take the opportunity to show you a real band and real music. But I want to sing some songs for you too."

First up Justin played "Cry Me a River" and then fan-favorite "Like I Love You." "He stopped for a second, claiming, 'I'm too old to sing this song,' but he laughed and kept going anyway," the eyewitness says.

He then played "What Goes Around Comes Around" and the Rolling Stones hit "Miss You." He began to play "Dead and Gone," but didn't finish it.

"He was totally into the entire performance. You could tell he had missed the spotlight and singing for a live audience - it's been four years since he's toured!" says the eyewitness."It was a great night."

"After JT's concert he came to Southern Hospitality for the second night in a row," a second eyewitness tells Life & Style. "He stayed until 4am!"