'Dear X. Thanks for your essay. You've spelled your name correctly, if not mine, and it's printed on actual paper. You've selected the correct alphabet, though the traditional order of letters appears to be unfamiliar to you. Your work indicates a high degree of facility with regard to Wikipedia and Allfreeessays.com, and you've obviously managed to find your way onto campus to hand in this piece. While I am impressed by these transferable skills, I must in all conscience suggest that actually reading the novel you're writing about might possibly be helpful'.
No, that wouldn't do at all.
So I'm always thrilled by people who write letters which express what they mean in the way they'd have spoken it. Larkin and Amis wrote hilarious letters to each other in a private kind of language. Hunter S. Thompson's complaint letters are terrifying, and Mark Twain (real name, Samuel Clemens) gave idiots both barrels. Pharyngula presents this one, in response to a quack medicine retailer.