When did the p--- word and the n--- word, that Frankie Boyle got criticised for using, get banned?

I have often heard the use of the words quite openly used by young asian and black teens, so can the words be used or is it some kind of offence? To be offensive isn't it the way the words used. I haven't heard the reference Frankie Boyle made but the same racist accusations are levelled when ever the words are used on TV and I am puzzled as to what is right or wrong..