H.I.F.
One of the best list articles I've ever read: 10 Devastating Author-To-Author Insults. Samples:
Twain on Austen: “Every time I read Pride and Prejudice, I want to dig her up and beat her over the skull with her own shin-bone.”
Wilde on Pope: “There are several ways to dislike poetry; one is to dislike it, the other is to read Alexander Pope.”
