Well, techinically every boss can be considered a coward from a certain point of view, because they don't face their victims directly but send hitmen instead, while providing for themselves an alibi. Only Vincent Basciano participated in a hit personally as a boss, as far as I know.
Willie Marfeo to Henry Tameleo:
1) "You people want a loaf of bread and you throw the crumbs back. Well, fuck you. I ain't closing down."
2) "Get out of here, old man. Go tell Raymond to go shit in his hat. We're not giving you anything."
