Eddie Murphy and Richard Pryor run a nightclub in the New York of the late 30s and find themselves at odds with both the Mob and the cops. If endlessly repeating the phrase "motherfucker" was intrinsically amusing then Harlem Nights would be the funniest film ever made.
Unfortunately, a real comedy needs a decent plot, interesting characters and some kind of creative context to work out of. This has none of these and it's all Eddie Murphy's fault because as well as being the star he also wrote and directed it.