Complex sentence: Mister Charlie is a pejorative expression used within the African-American community to refer to an imperious white man, or occasionally, a black man who is arrogant and perceived as "acting white".
Split into simpler sentences: Mister Charlie is a pejorative expression used within the African-American community to refer to an imperious white man. Occasionally, it refers to a black man who is arrogant and perceived as "acting white".