Refers to those of african descent. The black hen is most likely Mother Africa or simply one's mother and chicken refer to her chicks or chickens, children. It is a term very common in Trinidad (West Indies) and is used mainly in situations to refer to young girls of Afro Trinidadian descent who are steering down the wrong path. However in some cases, any one of Afro Trinidadian (male or female) descent may be described as one providing they are an adolescent or teenager. Adults use this term when correcting their children. However it is ok to use amongst friends in a joking manner.
"Black hen chicken (noun)"
1) What happen to you black hen chicken? I don't want you talking to that boy! (Parent)
2)Why black hen chicken so? Doh drink all nah all yuh! (Friend)
The examples above are in the local dialect of Trinidad.
It simply means:
2) Why are "black hen chickens" like that? Don't drink the whole thing you guys!