When you've killed your white owners and realize crops don't grow from singing.
Joking about slavery isn't appropriate when you remember that slavery wasn't abolished so long ago.
Black people are lazy and lack discipline and are useless.
Using any of those terms just feeds into a stereotype that doesn't exist any longer. People can make jokes, share stereotypes, tell false stories, but it doesn't change the fact that this is hurting millions of people. Have you considered widening your friendship circle to include a more diverse crowd?