I have a joke for you. What word begins with n ends with r and you don't want to call a black man ?
It sounds like you're making a disgusting joke about Black people.
The same context people use it in everyday. I don't mean any harm.
Stereotyping is not good because it leads to wrong notions about a particular community and on that basis, discriminating against it. Black people victimized by insults and stereotypes affect their self-confidence and make matters worse.
Language is there to express your thoughts and its quite impossible to fit in everything without hesitation and clarification.
You should consider the harm using racial slurs can cause before you joke about them. It's likely that there are Black people in your life that you care about. Would you want them to be hurt if they heard the way you use racist language?