In order to whittle it down we need to use the process of elimination.

If it is an actor that is well known and has (or even had) a prior reputation that would leave around 5-6 actors.

Then you pare down the ones that has been recluses the past few years and have also look gaunt and "out of it" when they rarely are seen in public.

When taking all of that into consideration you have the following:

Sean Penn
Mickey Rourke
Charlie Sheen
One of the Wilson Brothers (the blonde one that supposedly tried to commit suicide a while back)

I don't think you can put RDJ in that group b/c ever since he got himself cleaned up he looks like quite well, (even got himself pretty buff for Sherlock Holmes) and has become a fitness fanatic that does not drink, smoke, drugs, straight laced family man, etc... and he is seen at premieres and whatnot looking like he is on an even keel, etc...