Lady Gaga Wore a Prosthetic Penis at VMAs

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Little monster in her pants!

Lady Gaga pulled out all the stops to become male alter ego Jo Calderone at the MTV Video Music Awards in L.A. Sunday.

The pop provocateur (real name: Stephanie Germanotta), 25, didn't just wear men's clothing (including Armani men's underwear) and fake stubble in her "drag king" get-up: To complete the gender-bending transformation, Gaga wore a prosthetic penis, an insider confirms to Us Weekly.

The "You and I" singer stayed in character throughout the night at the Nokia Theater.

"I am from New Jersey," Gaga as Jo told Us backstage. " My family is from Palermo, Sicily and I am not a singer or a model or an actor or anything. I am just a guy."

And "Jo" had high praise for fellow pop star Britney Spears, one of the night's honorees, who rejected Jo's sexy advances onstage. "She is f***ing hot. Didn't you j*** off to Britney when you were a kid?"