Oops! … Britney Said a Bad Word

January 24 -- Pop princess Britney Spears, whose racy outfits often belie her squeaky-clean music, revealed that she also has a mouth that would make many a mother blush.

Before she took the stage Thursday at Brazil's massive Rock in Rio festival, the young diva was apparently furious with the way the concert was being run.

"Don't tell me they're just letting the audience fucking stand out there like that," she said, apparently not realizing that her mic was on and that her words were being recorded. "Oh my God … Let's hurry all, seriously. This is retarded. They told me they were going to do a vamp."

Luckily, the P.A. was not on, so the crowd was unaware of the star's rant.

"Vamp" is a stage term for music played repeatedly before an artist takes the stage — the 19-year-old singer didn't want to take the stage in silence. But her next comments were harder to understand.

"Oh, shit, oh, no, what are they doing!?" she shouted. "Oh, my pants are too short, I grew, I thought they were going to … I know, I'm not just going to stand out there, I thought they were going to fucking vamp! OK, thanks. This is retarded."

The pre-show freakout was inauspicious. Though her set began well enough, the packed house of Brazilians didn't take well to the giant American flag that appeared on a screen behind Spears during her performance of "Lucky."

The crowd began booing and chanting "Brazil."

The recording was first played on Los Angeles radio station KROQ.