A term used on Craigslist to denote a posting in a discussion forum that was so vile, so nasty, so rude, so off-topic, or, simply, so freakin' DUMB that it needed to be removed. Such posts are sent to the "Isle of Misfit Threads" in forum 1047.
"Keepposting here, Staff has Isled your posts...soon you'll be missing a handle!"