A large black person, with features similar as to those found in racist stereotypes i.e. exaggerated lip and ear size. The term originated as an insult towards these people due to the size and colouring of the African Garboon tree. Thick set tree limbs of dark red/brown or black wood.
You would call someone "garbongo" when they are clearly wrong.
Garbongo means that something or someone are lower then trash and deserves to be burned like the filthy garbage they are