Thank you, Cloak and Quaf, for the PMs. Well, this is certainly annoying - since chat accounts are different from forum accounts, throwing him/her off from here wasn't enough.
I've looked at the chat logs. Unfortunately, I don't have the power to ban him on chat (unless he's online) so I'll leave a PM for Richard. I'll also pop in intermittently in the meanwhile - and if any of you are online with him, please PM/whatsapp me immediately so I can say au revoir to this fanfiction aficionado.