Los Angeles [US Weekly] Britney Spears is on a tramp-age!

The latest man to fall into the hard-partying pop star’s orbit is Matt Encinias, a 21-year-old college student who tells Us Weekly the exclusive details of his twisted night with Spears in the latest issue.

In just five hours, Encinias went from being an extra in her latest video to pounding drinks and locking lips with the single mom of two in a rooftop pool at L.A’s Standard Downtown hotel.

Although Spears was expecting her two young sons to be dropped off at her Beverly Hills home at noon (as per her custody arrangement with their father, Kevin Federline), the singer had arranged to have the pool reopened at 2 am for the exclusive use of her group, which included then-assistant Shannon Funk and some hand-picked male extras from her video shoot.

“Britney was the first one to undress, and then everyone else followed,” Encinias tells Us. “I turned around and saw that she was topless and she had fake tattoos of flowers on her nipples from the shoot.”

“I was told all she wanted to do that night was kiss a boy,” the 5’10” California native continues. “And that’s what she did. Mission accomplished.”

It was when the alcohol started running low that an inebriated Spears, 25, suggested a game of Truth or Dare. “I was dared to get naked and get out of the pool and walk as though I was on a catwalk in a fashion show,” says Encinias. “Britney was laughing really hard.”

But what happened later when they went back to Britney’s hotel room? For more on Spears’ wild night at the Standard Hotel, including the latest details on her custody battle with Kevin Federline, pick up the new issue of Us Weekly, on newsstands this week.