John Cena went from ass-naked to looking like a good old-fashioned Greek philosopher in record time at the Oscars -- and the wardrobe change was actually caught on camera.
The wrestler-turned-actor was on hand Sunday for a pretty cringe-worthy bit where he was supposed to run across the stage naked for the Best Costume Design category ... which ended with JC shuffling across the stage with the winner's envelope covering his privates.
The whole gag here was that John was in his birthday suit, and he was there to highlight the best costumes in movies -- something Jimmy Kimmel had to come and help him with.