4. Christopher Moltisanti (The Sopranos)
Big T's power-hungry cousin, Chris (Michael Imperioli), was consumed by a number of troubles: envy, greed, hankerings for side-chicks, you name it, but most memorably, his drug and alcohol problems. Unfortunately, no amount of money or therapy were able to wipe him completely clean of his reliance on the two to deliver him some peace from his "family" feuds.
In fact, if you take a look back, cocaine and heroin were often the root of his most fatal mistakes (*SPOLER ALERT)—his being fingered for possession by undercover cop "Danielle," his fiancee's resulting relationship with the FBI as an informant, his final vehicular altercation with Tony (James Gandolfini), which could've been easily-avoided had the guy just chosen not to sniff-and-drive, and let's not forget him crushing his lady's pooch after sitting on top of her in a lifted state. Well, guess that was more fatal for the dog.