“We have read your manuscript with boundless delight, and if we were to publish your paper, it would be impossible for us to publish any work of a lower standard. And, as it is unthinkable that in the next thousand years we shall see its equal, we are, to our regret, compelled to return your divine composition and beg you a thousand times to overlook our short sight and timidity.”
[Not my rejection, alas; it was sent to a friend of Brian Doyle’s, who wrote about it here.]