[quote=Cuco]
Hmm. I don't think I've ever encountered this personally. I have been in certain situations where characters ignore specific things, sometimes for fair reasons, but I've never found anyone that was so bizarre as to just pretend everyone else just isn't there. That would actually be something to see.
[/quote]

Oh god, I wish I still had the log of a rp where this literally happened. Someone new joined a rp I co-GMed, a school for superpowered humans/supernatural beings - the sheet seemed ok, and one particularly friendly person decided to try interacting with the new character. 5 rounds of conversation starters and an exploded musical room later (with smoke everywhere), the new character hadn't even ACKNOWLEDGED any of it and went off to the school's surrounding forest because...hell if I know. I pulled the plug on that rp out of mercy. The new rper never returned, and four years later I'm still baffled as to why they signed up in the first place.

So yeah it does happen, and not to just that guy. Thankfully, that's the only one I've really ever dealt with. Your GM story, though - some people direly need co-GMs if only to not sound like a total idiot.