In November of 1905, an enraged Mark Twain sent the following superb letter to J. H. Todd, a salesman who had just attempted to sell bogus medicine to the author by way of a letter and leaflet delivered to his home. According to the literature Twain received, the "medicine" in question — called "The Elixir of Life" — could cure such ailments as meningitis (which had previously killed Twain's daughter in 1896) and diphtheria (which killed his 19-month-old son). Twain, himself of ill-health at the time and very recently widowed after his wife suffered heart failure, was understandably furious and dictated this reply to his secretary, which he then signed.
Transcript follows. Letter taken from the Letters of Note book, which you can read about here.
Nov. 20. 1905
J. H. Todd
1212 Webster St.
San Francisco, Cal.
Your letter is an insoluble puzzle to me. The handwriting is good and exhibits considerable character, and there are even traces of intelligence in what you say, yet the letter and the accompanying advertisements profess to be the work of the same hand. The person who wrote the advertisements is without doubt the most ignorant person now alive on the planet; also without doubt he is an idiot, an idiot of the 33rd degree, and scion of an ancestral procession of idiots stretching back to the Missing Link. It puzzles me to make out how the same hand could have constructed your letter and your advertisements. Puzzles fret me, puzzles annoy me, puzzles exasperate me; and always, for a moment, they arouse in me an unkind state of mind toward the person who has puzzled me. A few moments from now my resentment will have faded and passed and I shall probably even be praying for you; but while there is yet time I hasten to wish that you may take a dose of your own poison by mistake, and enter swiftly into the damnation which you and all other patent medicine assassins have so remorselessly earned and do so richly deserve.
Adieu, adieu, adieu!