Barnaby is one of the unlucky victims of Captain Hook. Having once made the mistake of addressing the Pirate as "One Hand Jones", he went on to pay for it with his life.
Before the Curse
As a pirate, Killian Jones went on to collect the rings of his murder victims, one case being when a man named Barnaby addressed him as "One Hand Jones". Because of this, Killian decided to kill Barnaby right in front of his wife, and kept the man's ring as a trophy. ("Birth")