Difficult people are no easier to deal with in electronic forums than they are in person. By "difficult" I don't mean "rude". Rude people are annoying, but they're not necessarily difficult. This book has already discussed how to handle them: comment on the rudeness the first time, and from then on, either ignore them or treat them the same as anyone else. If they continue being rude, they will usually make themselves so unpopular as to have no influence on others in the project, so they are a self-containing problem.
The really difficult cases are people who are not overtly rude, but who manipulate or abuse the project's processes in a way that ends up costing other people time and energy yet do not bring any benefit to the project.
Often, such people look for wedgepoints in the project's procedures, to give themselves more influence than they might otherwise have. This is much more insidious than mere rudeness, because neither the behavior nor the damage it causes is apparent to casual observers. A classic example is the filibuster, in which someone (always sounding as reasonable as possible, of course) keeps claiming that the matter under discussion is not ready for resolution, and offers more and more possible solutions, or new viewpoints on old solutions, when what is really going on is that he senses that a consensus or a ballot is about to form and he doesn't like where it's headed. Another example is when there's a debate that won't converge on consensus, but the group tries to at least clarify the points of disagreement and produce a summary for everyone to refer to from then on. The obstructionist, who knows the summary may lead to a result he doesn't like, will often try to delay even the summary by relentlessly complicating the question of what should be in it, either by objecting to reasonable suggestions or by introducing unexpected new items.
To counteract such behavior, it helps to understand the mentality of those who engage in it. People generally do not do it consciously. No one wakes up in the morning and says to himself: "Today I'm going to cynically manipulate procedural forms in order to be an irritating obstructionist."
Instead, such behavior is often prompted by a kind of insecurity, a feeling (not necessarily based in reality) of being shut out of group interactions and decisions. The person feels he is not being taken seriously, or, in the more severe cases, that there is almost a conspiracy against him — that the other project members have decided to form an exclusive club, of which he is not a member. This then justifies, in his mind, interpreting rules with maximum literalness and engaging in a formal manipulation of the project's procedures, in order to make everyone else take him seriously. In extreme cases, the person can even believe that he is fighting a lonely battle to save the project from itself.
It is the nature of such an attack from within that not everyone will notice it at the same time, and some people may not see it at all unless presented with very strong evidence. This means that neutralizing it can be quite a bit of work. It's not enough to persuade yourself that it's happening; you have to marshal enough evidence to persuade others too, and then you have to distribute that evidence in a thoughtful way.
Given that it's so much work to fight, it's often better just to tolerate it for a while. Think of it like a parasitic but mild disease: if it's not too debilitating, the project can afford to remain infected, and medicine might have harmful side effects.
However, when it gets too damaging to tolerate, then it's time for action. Start gathering notes on the patterns you see. Make sure to include references to public archives — this is one of the reasons projects keep records, so you should use them. Once you've got a good case built, start having private conversations with other project participants. Don't tell them what you've observed; instead, first ask them what they've observed. This may be your last chance to get unfiltered feedback about how others see the troublemaker's behavior; once you start openly talking about it, opinion will become polarized and no one will be able to remember what they formerly thought about the matter.
If private discussions indicate that at least some others see the problem too, then it's time to do something. That's when you have to get really cautious, because it's very easy for this sort of person to make it appear as though you're picking on them unfairly. Whatever you do, never accuse them of maliciously abusing the project's procedures, of behaving in a paranoid manner, or, in general, of any of the other things that you suspect are probably true. Your strategy should be to look both more reasonable and more concerned with the overall welfare of the project than they are, with the goal of either reforming the person's behavior or getting them to go away permanently. Depending on the other developers and your relationship with them, it may be advantageous to gather allies privately first. Or it may not; that might just create ill will behind the scenes, if people think you're engaging in an improper whispering campaign.
Remember that although the other person may be the one behaving destructively, you will be the one who appears destructive if you make a public charge that you can't back up. Be sure to have plenty of examples to demonstrate what you're saying, and say it as gently as possible while still being direct. You may not persuade the person in question, but that's okay as long as you persuade everyone else.
I remember only a few situations, in almost 30 years of working in free software, where things got so bad that we actually had to ask someone to stop posting altogether. In the example I'll use here, the person was not rude, and sincerely wanted only to be helpful. He just didn't know when to post and when not to post. Our forums were open to the public, and he was posting so often, and asking questions on so many different topics, that it was getting to be a noise problem for the community. We'd already tried asking him nicely to do a little more research for answers before posting, but that had no effect.
The strategy that finally worked is a perfect example of how to build a strong case on neutral, quantitative data. One of the developers, Brian Fitzpatrick, did some digging in the archives, and then sent the following message privately to a few other developers. The offender (the third name on the list below, shown here as "J. Random") had very little history with the project, and had contributed no code or documentation. Yet he was the third most active poster on the mailing lists:
From: "Brian W. Fitzpatrick" <firstname.lastname@example.org> To: [... recipient list omitted for anonymity ...] Subject: The Subversion Energy Sink Date: Wed, 12 Nov 2003 23:37:47 -0600 In the last 25 days, the top 6 posters to the svn [dev|users] list have been: 294 Karl Fogel 236 "C. Michael Pilato" 220 "J. Random" 176 Branko Cibej 130 Philip Martin 126 Ben Collins-Sussman I would say that five of these people are contributing to Subversion hitting 1.0 in the near future. I would also say that one of these people is consistently drawing time and energy from the other 5, not to mention the list as a whole, thus (albeit unintentionally) slowing the development of Subversion. I did not do a threaded analysis, but vgrepping my Subversion mail spool tells me that every mail from this person is responded to at least once by at least 2 of the other 5 people on the above list. I think some sort of radical intervention is necessary here, even if we do scare the aforementioned person away. Niceties and kindness have already proven to have no effect. dev@subversion is a mailing list to facilitate development of a version control system, not a group therapy session. -Fitz, attempting to wade through three days of svn mail that he let pile up
Though it might not seem so at first, J. Random's behavior was a classic case of abusing project procedures. He wasn't doing something obvious like trying to filibuster a vote, but he was taking advantage of the mailing list's policy of relying on self-moderation by its members. We left it to each individual's judgement when to post and on what topics. Thus, we had no procedural recourse for dealing with someone who either did not have, or would not exercise, such judgement. There was no rule one could point to and say the person was violating it, yet everyone except him knew that his frequent posting was getting to be a serious problem.
Fitz's strategy was, in retrospect, masterful. He gathered damning quantitative evidence, but then distributed it discreetly, sending it first to a few people whose support would be key in any drastic action. They agreed that some sort of action was necessary, and in the end we called J. Random on the phone, described the problem to him directly, and asked him to simply stop posting. He never really did understand the reasons why; if he had been capable of understanding, he probably would have exercised appropriate judgement in the first place. But he agreed to stop posting, and the mailing lists became useable again. Part of the reason this strategy worked was, perhaps, the implicit threat that we could start restricting his posts via the forum's moderation features. But the reason we were able to have that option in reserve was that Fitz had gathered the necessary support from key people first.
 For an extended discussion of one particular subspecies of difficult person, see Amy Hoy's hilariously on-target https://slash7.com/2006/12/22/vampires/. Quoting Hoy: "It's so regular you could set your watch by it. The decay of a community is just as predictable as the decay of certain stable nuclear isotopes. As soon as an open source project, language, or what-have-you achieves a certain notoriety — its half-life, if you will — they swarm in, seemingly draining the very life out of the community itself. They are the Help Vampires. And I'm here to stop them..."
 I recently learned the delightful and very useful term sealioning, which refers to a particular type of filibuster: repeated insistence that more evidence is needed, or asking endless questions with the alleged purpose of clarifying but with the actual purpose of delaying. See https://en.wikipedia.org/wiki/Sealioning. Persons engaging in sealioning may not even be consciously aware that their behavior is not actually good-faith participation in debate.