Green’s Dictionary of Slang

nago n.

[Nago, a person born in Nago, a Yoruba-speaker; many such people were transported from Africa as slaves]

(W.I.) a very stupid, ugly or notably dark-complexioned person.

[WI]L. Barrett Sun and the Drum 16: To this day, when one person in my community refers to another as ‘Nago’, it means that the second person has done something foolish.