Some blame the outfit. Others point a finger at Sarah Silverman. Still others question MTV's judgment in the first place to open the show with Britney Spears.
But whatever the reason, the pop star's lackluster performance of her new single "Gimme More" is getting universally bashed the day after her supposed "comeback" in a sparkly black bikini and blonde weave on Sunday's Video Music Awards.
"Britney was supposed to wear a matching corset that she opted out of wearing at the last minute," a source tells PEOPLE. "She was just plain nervous because of all the hype and she's embarrassed."
Adds another, "She looked disappointed" backstage after the performance.
"She was extremely nervous. It's been awhile since she's done this, and she was performing in front of all her peers, on live TV. She just got out there and froze," says a source who was also backstage as well as at rehearsal (watch the clip). "People who were at rehearsal saw something else. It was good. It really was."
In addition to the barbed comments (everyone from Whoopi Goldberg to The New York Times piled on), conspiracy theories abounded as to why Spears appeared out of it and uninspired.
Fan site BreatheHeavy.com and photo agency X17 speculated that Spears was thrown off after hearing Sarah Silverman rehearse her monologue (which ripped Spears and called her kids "mistakes").
But Silverman's rep tells PEOPLE it's untrue: "Sarah never rehearsed her full monologue ahead of time so no one knew what Sarah was going to say except for Sarah."
On another celeb blog, Oh No They Didn't, a reader posted supposed photo evidence that Britney was wobbling on a broken stiletto heel during her performance.