Okay let's get to the bottom of this.
First off I screwed up, it's actually called 'TACHY goes COVENTRY'. Now to me that name still doesn't make much sense. Apparently it doesn't make sense to other admins either because there is a thread devoted to this over at the vbull forums.
I believe it refers to being sent to coventry.
Cov·en·try: n.
A state of ostracism or exile
Its a UK thing as I understand it.
The setting puts a user on global ignore. So he can post, but he's the only one that can see the posts. Typical scenarios look like this.
user1: What happened to user2? I clicked his new thread and it said the thread didn't exist.
user2: Nothing happened to me I'm right here...
user1: Oh he must be banned
This is a great setting for spam bots because they continue to add stats to an admin's bottom line but never accomplish their spam mission.
For users this isn't so great of a setting. Within a day or 2 they figure out they've been sent to exhile island and just get pissed.