Britney was drunk

Britney was allegedly drinking margaritas rather than working to get her moves down while rehearsing her slut-zombie "performance" this weekend, and her dancers were literally praying for salvation before their performance -- because they knew it was going to be a disaster. I guess Britney showed up to her Saturday rehearsal a few hours late, and she did it "with a frozen margarita in her hand." HA!

And when she actually did manage to practice, it was clear that she would bring the whole number down with her. "The dance number was spectacular -- without her," says a spy. "Britney ... refused to do anything. The more complicated dance moves had to be erased because she couldn't do them."

As for her widely-ridiculed wardrobe choice, Page Six says that MTV had picked out a corset outfit, but Spears nixed it as "not sexy enough." Oh, Brit.