What is the difference between a black man and a nigger?

This is the "Deep Cover (1992)" movie clip beginning scene of the DEA special agent (Charles Martin Smith) interviews three colored police officers (Clifton Powell, Lionel Matthews, and Laurence Fishburne) asking the question, "What is the difference between a black man and a nigger?

Deep Cover (1992)
https://www.imdb.com/title/tt0104073