Comes from the word Deceleration meaning slowing down.
(Decelerated) is used as an insult less specific to certain group of people and focused on the act or behavior of someone instead of the word "Retarded" since retarded meaning is seen as an adjective for disability which is insensitive.
Someone who is addicted to obtaining money and building wealth. A money addict and fanatic. Breadheads often work more than one full-time job, and some even participate in illicit activities to "obtain the bread".