A recent post from Magician's Manse got me thinking about PvP again. It sounds like the monk player there was being an asshole and a bully, though Ian doesn't want to come out and say it. I don't play in the Flailsnails / Constant Con Google Plus games, so I don't have to worry about anyone's emotions.
I think referees ought to step in to prevent bullying between players (not between characters), and that the most effectively way to prevent it is not to have a long talk about expectations and people's emotions, but to simply and firmly assert authority over the bully. Basically, you make an injunction, and then refuse to negotiate or argue about it. Bullying people is all about getting them to accept your authority over them as somehow deserved or legitimate, and a common tactic when one's victims resist is to negotiate or argue, especially if you can present yourself as an expert or at least the best qualified to discuss an issue. A bully wants to provoke you into an obviously emotional and irrational outburst which allows him to assert that he is the most rational, most level-headed, not so overcome by emotion, etc. which allows further bullying and control to be exerted. The best response here is not to give into that, and get as angry as you feel is appropriate. It's also why it's always easier to stand up for someone else when they're being bullied rather than for yourself when you're being bullied, because you haven't got someone else directly asserting their authority over you to prevent you from resisting them.
When you assert authority over them and then refuse to negotiate or argue about it or to allow one's self to be trivialised emotionally, a bully's options reduce to withdrawal / submission or violence. Most won't escalate to violence (and you probably shouldn't be gaming with them anyhow unless you like being threatened constantly). Most will submit, even if only half-heartedly.
The problem in the above example really happens well before there's any trouble, when the other PCs are acting from a position of good faith, but ignorance, and the bully has them submitting to his authority using a plausible pretext (I'm the highest level; this is my home game). Especially in online games or games where you're not face to face (like the Flailsnails games), this is super easy to get away with because all the rich social cues you use to figure out that someone is the interpersonal equivalent of a fluttering scabrous strand of menses are suppressed, either because it's all text, or there's only tiny boxes of people's faces with so-so microphones and lighting.
Also, the referee should have stepped in from the get-go and said "This is a dungeon for first level characters, I'm looking for first level characters. This isn't a first level character," to the troublesome player. I'd bet money he was pressured into letting the bully's character participate by the bully. This is no doubt exacerbated if the bully can talk to the referee one-on-one and strip away any third parties who will help the referee resist the bullying.
Cutting down assholes is pretty fundamental to keeping gaming a living hobby.