Ummm - you forgot to mention that you should be as righteous as possible - you know - like spending your valuable time researching their past to expose some dumb stuff they did - then using bible quotes... BIBLE QUOTES!
You got that right! It was time well spent! I certainly hoisted some guy on his own petard when I did that! Who was that guy, anyway? Walked right into it, he did.
As for the original question I feel a simple "Good day, Sir!" is a courteous way to express my distaste.