"racist" question

Okay so I hear a lot of my friends say "nigga" and it kinda makes me mad because they're white. My mother is half black which makes me 25% black so I hear it in my family all the time..but it doesn't make me mad because they're black.
Also, I don't look black even though I am so I've always been uncomfortable using the n word.
But if I did, and somebody got offended, would me being 25% black justify it? 
Sorry this is so off topic but I don't know who to ask