This discerns from a slur form and the slang form of the word "nigger". If pronounced with a hard 'R', its considered racist. If its pronounced with an 'a', phonetically spelled 'nigga', the term is not meant as racist rather as a sort of nickname, like buddy or ace.
Guy 1 "that right theres a typical nigger"
Guy 2 "whoa whoa, hard on the r"