The "N" word.
And I especially hate it when Black People use it. "I can use it because I'm black!" That's the stupidest thing I've ever heard. It's a word synonymous with oppression and racism, and you use it without even thinking. And it's even worse when white people use it; have we really forgotten that, only 50 years ago, people were flinging this word around as an insult? Now, we use it like a compliment almost. It's disgusting. Any person that uses that word deserves to be slapped in the face so hard, they strain their neck muscles.
Also, I've heard "Jew" being thrown around as an insult in my school. This IS 2010 in America, right? And not 1936 in Germany
And Misuse of the word "Gay". This is one of the main reasons I cringe at Yahtzee's videos. I've been called "Gay" several times because I act weird; While I am not opposed to the Idea of Homosexuality, I am straight. "Gay" has become synonymous. and interchangeable, with "Lame". Whoever uses gay in this context deserves a Swift kick in the crotch.