Back in the late 60s-early 70s this word was in it's most common use here in America. More often than not I recall it being written as 'boo koo' or 'boo coup' and pronounced about half the time as 'bow kew'. The word is French meaning many. I suspect that the citizenry of Viet Nam picked it up from the French military during their disastrous time there. We replaced the French and our soldiers picked it up from the Vietnamese. The word then traveled here via our returning vets and gained some popularity for about a decade, that is from my perspective in Washington State near an army base. Then it all but died out around here for the next forty years. Recently I have been hearing it used among younger people and now here in the DU I have today seen it as 'buku'.
There is no real point to my observation, I just found the local history and recent resurgence of the word fascinating.