Hat-tip to +Luis Rocha
not only for fascinating comments in the thread below, but also for pointing us to this picture - Caravaggio's 16th century depiction of Judith beheading Holofernes
as a precursor of some of the bits of rap that one might consider less savoury.
Here's the story: Judith got Holofernes, a Syrian general, drunk, led him to bed and there, at his most vulnerable, beheaded him as shown (http://en.wikipedia.org/wiki/Judith_Beheading_Holofernes_(Caravaggio)
). Caravaggio used a prostitute as a model for Judith. Look at her expression - do you see much pity or distress there? Maybe a concern not to get her nice white blouse dirty.
As +Luis Rocha
points out below about Caravaggio, "The commissioned work he created for various churches, was often returned to him with a request that it be repainted in a less sinful manner."
Maybe there are examples of commissioned rap, maybe for commercials, like this - sent back with the request it be toned down?