Rarest passport would have to be of the Sovereign Military Order of Malta. the Order of Malta is a Roman Catholic institution or order which goes by the motto of “Defence of the (Catholic) faith and assistance to the poor.” It is active in 120 countries, where it helps to care for people in need through its medical, social, and humanitarian efforts.
This order is the means to the rarest password with only 500 in circulation currently making it the most exclusive passport in the world. This is granted only to the members of the Sovereign Council (heads of the government), members of its diplomatic missions.
— Karim (@KIMO79KIMO) December 27, 2014