Gary Oldman apologized again -- this time on Jimmy Kimmel -- for telling Playboy that everyone has used the n-word and talked about "f**king Jews," but Kimmel raised the question ... how do you know if a great actor is being sincere?
Oldman talked for a long time, saying he was sorry for using the words, although he never addressed the sentiment. On Wednesday, he apologized to the Jewish community, but didn't address the African American community.
Oldman has been backtracking ever since the article came out ... where he defended Mel Gibson and Alec Baldwin and postulated that everyone drops a racial slur every now again.
So we gotta ask ...