EDIT: Or maybe DDoS. That site deserves it.
You say we should do a DDoS to them? That would just be like being worse than the spammer. We need to try figuring this out in a more civilized way.
Blocking posts with ANY html is the way to go. I'll bet this bot doesn't even know that we don't support HTML. Maybe blocking the username that the bot uses would be good too, as it wouldn't be able to do anything. Someone could maybe register under that name, making it unable to use it?
EDIT: Anyone have a clue why this bot seems to post fragments of sentences somewhere in the HTML? I can't see what it's supposed to be. The sentences can't be connected either, like it's just a buncha rambling.