I'm naked a lot. And I bounce around frequently; I'm a big frolicker. So I think it would be best for a beautiful woman to play me. It just makes sense. And we want the movie to make money, don't we? No one wants to see a naked Ernest Borgnine on screen.
I actually look more like Salma Hayek than I do Ernest Borgnine, anyway. It's the taut behind and lack of googly eyes.
Short Answer: Fassbender?