Before Britney Spears took to the stage of 'Jimmy Kimmel Live' to perform her new single, Johnny Knoxville shared footage of the 'Jackass 3D' gang subjecting the pop star to horrific levels of human excrement.

Roll tape. She claims she's not afraid of "poo-poo." But what about the "poo cocktail supreme"? They lock her in a porta-potty lodged between bungee ropes. As the portable toilet soars through the air, bouncing up and down, human waste splatters throughout the inside, across the camera and all over Spears.

Perhaps the grossest aspect of the ordeal is that she keeps screaming -- so her mouth is open the whole time.