From a compounding of "nigger" and "honky". Used to describe a person fitting the firstdescription acting as a person fitting the second.
"He's got qualifications, a job, property & he plans for his kids..Is he going nonky on us or what?", or
"Who's the new nonky on reception? He speaks better english than I do!"
A black man or woman, walks around trying to impersonate a white Caucasian individual. By attempting to roller skate, race cars, play golf or swim. Etc