N-Word

George Carlin famously mocked the Seven Dirty Words You Can't Say On Television. Those words, however, merely offended bourgeois sensibilities. Not even the inveterately irreverent Carlin would dare take on The Word That Dare Not Say Its Name. 

I refer, of course, to the dreaded n-word. Even the etymologically unrelated "niggardly" has laid careers to waste and reputations to ruin. (For more on that, see the Wikipedia link.) Some sound waves emanating from vocal cords really are off limits.