Timberlake, who won the award for favorite male singer, was slimed both at the beginning and end of the show.
During the opening number, Timberlake, dressed in a tuxedo and an orange scarf, sang: "You'll never get a drop of slime on old J.T." – but was soon covered with it.
Other stars who got drenched with the green stuff included Mandy Moore, Tobey Maguire, Steve Carell, Vince Vaughn, Chris Tucker, and Jackie Chan. Even Nicole Kidman got slightly slimed when she accepted the award for the animated movie Happy Feet. (The actress, who voiced a character in the film, was there on behalf of the film's director, George Miller.)
The show, which featured performances by Gwen Stefani and Maroon 5, also included a daredevil bungee jump by stuntman Ron Jones, who plunged into a giant vat of green slime from a height of 225 feet.
Early in raucous show, Charlotte's Web star Dakota Fanning won for favorite female movie star and the Black Eyed Peas won for favorite musical group.
"I consider all of you my friends!" said Fanning, who was presented with the award by Blades of Glory stars Will Ferrell and John Heder.
Other awards went to Ben Stiller, who took home the night's top honor, the Wannabe Award, Adam Sandler for favorite male film actor and American Idol for favorite the TV show. Idol judges Randy Jackson and Paula Abdul were on hand to accept the award.
Randy asked Paula, "Where's Simon?" Paula responded, to much squealing from the crowd, "Who cares?"
Sandler, who won for favorite male movie star in 2003 and 2005 as well, accepted the award while speaking in his Happy Gilmore voice and thanked the crowd "for not making fun of me for talking like this every speech I do."
Fred Prouser / Reuters / landov
As for burping champion, Timberlake lost the the title after he was challenged by the entire 12,000-person crowd to a burp-off. Together, everyone at the Pauley Pavilion – with the help of some special effects – defeated the singer with a massive ensemble burp.
"Tonight I went head-to-head with every kid in the audience and I don't know if I stood a chance," Timberlake said backstage after the show. "They came in strong and I gave it a go but it just wasn't good enough."
At the end of the evening, Timberlake, with the help of Vince Vaughn, used a "detonator" to release a giant surge of slime that came up through the floor, spraying the actors and much of the audience and.
Awards are determined by kids who vote to pick the winners. Approximately 40 million votes were cast this year, according to Nickelodeon.
Reporting by REAGAN ALEXANDER and JEN GARCIA