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Christina Aguilera knows a bit about getting "Dirrty".

Since her October split with husband Jordan Bratman, the singer, 30, has been getting plenty rowdy with her new 25-year-old beau, Matthew Rutler.

An insider tells the new issue of Us Weekly (on stands now) that the Burlesque star and the production assistant even had sex in a bathroom at a recent family gathering.

"Her friends are fed up," the source says of Aguilera's recent antics, which included a New Year's Eve blowout fight with her mom and a booze-filled night of crying at L.A. club The Dime in January. "Nobody can get through to her. They think she's trashy. And her ego is out of control."

And at least one Aguilera pal isn't confident things will improve any time soon.

"She's really spiraling," says the source. "I would be shocked if she's not in rehab in the next month or two."

For more on Aguilera's out of control behavior -- including how her three-year-old son Max is doing -- pick up the new issue of Us Weekly, on stands now.