A moment where ignorance overwhelms the logic of an otherwise rational negro, and that ignorance then overwhelms another rational negro nearby until all negros in the vicinity are in a "nigga moment".
We were in the middle of a grief counciling session when a black girl got up and started talking about how she felt and how she didn't like some of the people she works with and about how we have "cliques" all the while getting further and further off topic and louder and louder in a full blown "nigga moment"... Next thing I know all the black people in the room are yelling at each other. Hence a "compounding nigga moment".