I thought you might enjoy this article that begins, "Sigh. Authors just don't insult each other like they used to." It goes on to quote thirty hilarious author insults, including Dylan Thomas dissing Rudyard Kipling, Elizabeth Bishop dissing J. D. Salinger, and William Faulkner dissing Mark Twain. Lord Byron said of Keats, "Here are Johnny Keats’ piss-a-bed poetry, and three novels by God knows whom … No more Keats, I entreat: flay him alive; if some of you don’t I must skin him myself: there is no bearing the drivelling idiotism of the Mankin.” And Friedrich Nietzsche called Dante Alighieri, "A hyena that wrote poetry on tombs."
Good fun (though I don't suppose the insulted authors would agree)!