In an age where celebrities are styled to the point that they barely seem human, it's kind of refreshing to see one who just totally can't be bothered. At the same time, however, when you consistently leave the house looking like you've just put on every random bit of clothing you can find, people are going to start to wonder.
To prepare for Last of the Mohicans he spent time living off the land and learned to skin animals. For My Left Foot he spent all day every day in a wheelchair, earning him no friends from the crew members who hand to carry the chair over cables and the like on the set. For The Ballad of Jack and Rose he lived for a time in total isolation. I don't even want to think about how he got into character for Bill the Butcher. There's commitment to the craft and there's a cry to be committed. Plus, anyone who wears that suit can't be entirely sane.
When it's all said and done, Mickey Rourke will at least be able to say that he did it his own way. The jury's still out on whether that's a good thing or a bad thing. Although I was rooting for Sean Penn to win Best Actor, part of me was disappointed about not getting to hear Rourke's speech because I know it would have been epic.
As great as he was, it's amazing that Brando's career lasted as long as it did, given that a director never knew on any given day which Brando was going to show up - would it be the passionate genius who would turn in a great performance, or would it be the spoiled star who would come in late (if at all), mumble a few words, mess around for a while, and leave you with nothing usable for the day? Still, it can't be denied that when he was on, he was on.
Everyone else on the list is really just eccentric; Kinski is probably the only one who was certifiably insane. I mean, when even Werner Herzog, who is himself teetering on the edge of the insanity chasm, thinks you're nuts, you're probably pretty far gone.