This is a customized version of the word Hillbilly, but used in reference to the people living/born in Kingston, Jamaica.
A Kingbilly is one who is so closed-minded, backward and antiquated in thought/ideas in general that they border on 'being dim'.
The word is generally used in insulting terms, as to refer to a person as unsophisticated and backwards, or to say you come from the 'ghetto/poor/country' areas.
"How can a black person not like black people? What a fu%^ing kingbilly"
"Wow, Jen is definately nowhere near bright, she's a border kingbilly"
"You ARE NOT coming with me to ClubZ looking like a kingbilly"
"You live in Tivoli? You're practically a kingbilly"