kaffir
An Arabic word for someone who doesn't believe in God, and in South Africa it got twisted into the worst insult for black people. It's like being called a dog, but worse.
My mom said, 'You're a kaffir!' because I didn't clean my room.
My brother got called a kaffir for eating my lunch.
My neighbor screamed 'Kaffir!' because my dog barked at him.