A fat crackhead
You can always tell when a drug addict has a long history of success by their weight. This is true no matter what the drug is, but is especially true for drugs like crack which reduce the appetite and physiologically cause the user to lose weight rapidly. But even with other addictive drugs that don't have these qualities (like heroin), an unsuccesful or only marginally successful user will have to spend all of their time making money for the drug, searching for the drug, buying the drug, using the drug, and starting again before they fall behind. The end result is that there is no time or money for food, and no interest since eating does not help advance the user's primary (usually sole) goal. So, a fat drug addict is a successful drug addict - at least if you don't consider that a contradiction in terms.