Britney Spears flopped at the MTV Video Music Awards, because she turned up for rehearsals more than four hours late and was drinking alcohol, according to reports. The singer disappointed fellow performers and audience members at the Las Vegas bash on Sunday (09Sep07) - her first major appearance in four years - with a rendition of new single Gimme More that was described as "nervous" and "shaky". An MTV source claims awards show bosses were furious when the singer missed her 1pm rehearsal on the day of the show. The insider tells the New York Post's gossip column PageSix, "She didn't even get to Las Vegas until 4:30 p.m. It was ridiculous. The production people at MTV were freaking out. Nobody can tell Britney what to do anymore. No one can control her. She is a mess. "She went to her hotel room and ordered a bunch of food and some frozen margaritas. She came down an hour later with a frozen margarita in her hand. "The dance number was spectacular - without her. When the stand-in was rehearsing with the dancers, in the hours they were all waiting for her, it was amazing. Then Britney showed up and refused to do anything. The more complicated dance moves had to be erased because she couldn't do them." The source claims Spears also chose her own underwear-inspired stage outfit, adding, "MTV wanted her to wear a corset outfit. It would have looked great and covered a lot of things up, but she hated it and didn't think it was sexy enough."