Vulgar idiom with American origin is typically used to imply that sexual activity with an African American or a black person is so enjoyable that one will exclusively seek out black partners in the future because of that.
Likely to harken back from taboos surrounding
African Americans during the Antebellum period in
United States history. During this period, large amounts of stereotypes existed around
African Americans, many, also sexual. Racist ideas were held like that black men were considered to be animalistic and unable to control their sexual urges, which made having a romantic relationship with a black man, especially as a white woman, extremely taboo. All southern states had anti-miscegenation (anti-interracial marriage) laws, which weren’t abolished until June 12, 1967, by Federal law.
Many kinks surrounding black men specifically, like many kinks, are rooted in older taboos, which are now gone.