I edited my post a bit...could you change your quote to reflect that? Thanks.
I would still agree with you if that didn't just remind me of a real life scenario where in a private school I went to, we all loved the teachers with charm like that haha.
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If the teacher is to get in trouble here, then I think the student should also. It's quite different.
So yeah I agree that words have different meanings on context. No one is so shocked when black people say the word in question, they are when white people do.
I was playing Destiny and, I guess being British, I sounded white. All 5 people were quoting rap lyrics, and after another thread on gaf I decided to quote others (including the word nigga of course). Two got insanely upset, one left the party, and I was grilled on how I couldn't say it being white. I made sure to say -a and not -er too.
Then they called me a liar when I said, "while it shouldn't matter if you're rational, I'm not" and they checked my profile to confirm.
In the end they ended up saying "well you sounded white - bla bla bla".
So all in all I think it's best to just not bother trying to offend anyone, there are many other words I can use instead I guess.
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The mam in the OP does deserve some sort of disciplinary action here anyway. Though if he really did have it said to him so casually on many occasions and he wanted to join in on the joke, it just makes me sigh at that.
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Without trying to sound insensitive, I think racial slurs will eventually go their way to not be so taboo in the future. The same way blasphemy isn't anymore. Even when that happens I'll still remember all the pointlessness of taking an incredibly offensive word and making it a cool thing to say (if you have a high enough melanin content).
No one say reverse racism though haha
https://www.youtube.com/watch?v=dw_mRaIHb-M