1669: Renowned diarist Samuel Pepys had the good sense to stop writing when his eyesight failed, unlike many other famous writers who kept on pushing the pen long after the cancer ate their talent. He wrote about one of the early Slushpile Bonfire Days that got out of control.
1790: The United States signs the first “Fsck You Fanficcers!” bill into law, forcing homobsessed hacks to wait 14 years before peddling their derivative smut. Unless the work was first published outside the US. In the first knockoff edition of Oliver Twist, “Fagin” was a verb.
1977: Legendary schockmeister William Castle finally stopped making terrible movies, and marketing them with spectacularly awful gimmick campaigns like “Illusion-O” and the “Fright Break”.
2000: International Slushpile Bonfire Day staves off criticism about pollution by trading carbon credits with World No Tobacco Day.
2005: Former FBI Deputy Director W. Mark Felt ruins a perfectly good mystery by admitting he was “Deep Throat” in the Watergate scandal.

I’m surprised that you didn’t mention that Timothy Leary joined the great slushpile in the sky on this day in 1996. Besides his finally stopping writing, it also buggered the ambitions of another writer: technoweenie favorite Charles Platt had been assigned to cover Leary’s decline by Wired, seeing as how Platt was a customer of the now-defunct cryonics company Alcor and Leary had made noises about having his head cryogenically preserved. From several reports, Leary and his assistants decided not to go that route because of Platt’s obnoxious attitudes toward such preservation, including allegedly loudly complaining about when the old bastard was going to kick off. (Platt still writes about cryonics, most recently for Make about a year ago, but when Wired was sold to Conde Nast, the new management decided that giving such leeway to prima donna writers wasn’t in its best interests.)