Justin Timberlake attends "El Hormiguero" TV show on November 28, 2011 in Madrid, Spain. Credit: Juan Naharro Gimenez/WireImage.com

On Thursday, Justin Timberlake rocked his soon-to-be-married body in Las Vegas -- for his bachelor party!

Set to wed Jessica Biel this year, the singer-actor, 31, was the guest of honor among a group of 20 men who "took over the dance floor table" at Tryst nightclub at the Wynn Las Vegas, a rep for the venue tells Us Weekly.

Wear a bowtie and a fedora, the Trouble With the Curve star and his posse sipped cocktails -- plus Timberlake's own liquor, 901 Tequila -- as they grooved until the wee hours to the sounds of DJ Spider. "The group was very polite," the rep says.

(Another star at Tryst Thursday? Ryan Seacrest, hanging out separately with two pals, by Tryst's 90-foot waterfall.)

The crew was also spotted at Surrender Nightclub at Encore and Sinatra Restaurant at the Wynn. Although Surrender -- an outdoor pool venue -- was packed with models, Timberlake "was a good boy," an eyewitness tells Us. "It was just him and his guys."

Back in January, Us Weekly broke the news that Timberlake  had proposed to longtime love Biel, 30, in the mountains of Jackson, Wyoming in late December 2011.

Dating for five years, the couple have been completely tight-lipped about when and where they'll wed. Back in July, Biel said she had done "almost nothing" to prepare for the big day.

"I'm just enjoying being engaged," the Total Recall star explained. "I do feel like there is a lot of time and nothing needs to be rushed."