John Gotti. Should've never risen above Soldier. He was basically a street thug who managed to somehow get Neil's favor and ended up taking down the Family and beginning the demise of the Mafia with his stupidity, wanton and reckless behavior, and flippant way he treated the threat of the Feds and the way he courted the media.

The guy was practically a self made rat. I mean, he wasn't a rat but for all the juicy info his big mouth gave the Feds he might as well have been a rat. For as much as he talked and got so many other guys in trouble because of his mouth, he might as well have been wearing a wire.