"Nigger" depends totally on the context. It is not racist at all if (mostly) black people calling others ( not only blacks ) that, because they don't mean it in a racist way. This is not so much possible for "retard". There are words in english that are much worse. Most people feel nothing but hate if they use the word "pedophile" although that one isn't automatically a child molester, still, they seem not to see the difference.