Slurs

Why do (for example) black people use slurs and expect that people won't start to use them aswell.

Lets go like this, I didn't hear about n word till i was 14 last year of 8th grade when some black kid started SCREAMING it at everyone. He got mad i think because someone took his pencil (idk don't remember correctly).

Like if people continue using the word it will be used obviously. 

AND NOT TO MENTION WHY ARE PEOPLE USING SLURS THAT ARE AGAINST THEM??? LIKE WHAT THE FUCK