Was this movie threatened with an NC-17?
I think it was given that the shooting of Curtis by its very nature would be rated so for "bizarre behavior". Shooting someone outta jealousy is not normal behavior at all. It's rather bone-chilling. Plus the focus on Fresh's psyche following the killings makes this NC-17, kinda like the black version of "Requiem for a Dream" (althoguh that movie came 6 years after this movie).
For lack of a better example, "Fresh" is similar to "Pulp Fiction" scene where Marcellus gets raped by Butch.