Dressed in a pair of feathery white wings with his rear end mostly exposed, the comedian crashed into an overhead obstacle and was lowered directly into Eminem's lap in the audience, his hindquarters in the rapper's face.
"Is the real Slim Shady about to stand up?" chirped Bruno.
Eminem seemed visibly upset by the encounter and members of his entourage roughly removed Baron Cohen as Eminem struggled to get out. But it was unclear if Bruno and MTV wound up the rapper, or if he in on the elaborate joke.
Eminem acted visibly upset at the mishap, saying: "Get this (expletive) off me" and turning his face away in disgust. He then stormed out with his entourage in tow - and cameras rolling - and beat a path for the exits.
Bruno's descent to the audience was included in earlier rehearsals, but Eminem did not take part in that piece of the run-through.
As the rapper stormed off it sounded as though he was wearing a microphone, and cameras were in position to record his fast exit, but he was not seen or heard from again.