Every once in awhile you'll hear about a beloved website whose host has taken it down out of frustration with having to deal with Internet thugs. Internet thugs are, thankfully, not very common, but there are enough out there that they can wreck the experience in trying to admin a website.
So what is an Internet thug? An Internet thug is basically a "griefer". Someone who gets off on trying to anger and upset other people. They do this in a variety of ways and the most common way is to take advantages of loopholes or gaps in a website's forum system.
For example, when we designed the blog community JoeUser.com, we allow users to "blacklist" people. So if someone is causing them anguish, they can make them go away. Now, the person can still try (with a different IP address) to come back as an anonymous user but the user can then make their blogs require a UserID to post and at that point, the griefer is usually stopped in their tracks.
But many sites don't have that level of protection. Some news systems only support anonymous commenting or no commenting at all (at which case, much of the enjoyment is taken away if no one can even interact). On such sites, the thugs can go wild.
Other sites have more protections but "moderators", wizops, and other sub-administrators don't have complete access to them. That can enable a thug to target a particular moderator to try to get rid of them. And most volunteers have a lower threshold of pain before they'll quit.
For me, when faced with a "flight or fight" instinct I am inclined to go with the latter. I've been running on-line communities for twenty years (literally, 1985 with Commodore 64 based BBSes on up). I've seen these guys and they typically are serial griefers -- they get off on it so they keep doing it over and over again. I've found that the only way to deal with them is use all the admin powers at my disposal to make it painful for them as well. Most admins I've met tend not to want to play dirty or take the gloves off. The griefers count on that and hence can play their sadistic little games with impunity.
But like I said, I play rough. If someone's griefing me, I'll get nasty. Instead of just removing their post, I'll edit their post. And if that doesn't discourage them, I'll eventually start posting their IP address. And if that doesn't work, there is a lot more uglier stuff (particularly if the griefer doesn't live in the US) that I can do. But usually post editing is enough.
For example, if a griefer writes: "You're a pathetic asshat, (user's real name when possible) . You should stick with having sex with your (insert relative) ." I will change it to say (with their real name as the responder) "I wish I was a girl. Sometimes, when no one is around, I like to wear a dress. Not having any genitalia makes me confused sometimes about what I should do and that's why I act out. Can you forgive me?"
Your ability to deal with griefers is only limited by your own conscience, your affiliation with the site (if you're a moderator and not an admin, you should be talking to the site owner before you start wreaking havoc, the site owner might be better equipped to deal with the griefer), and of course your real world resources. In my case, we have lots of lawyers so any would-be blow hard making legal threats can learn the hard way just how nasty the US legal system can be, especially to someone skirting the boundaries of cyber-terrorism. Which also means you should keep a log of any posts that person has made for use as future evidence if necessary.
Griefers rarely get bored. They get off on trying to hurt other people. But they're usually stupid, lazy people who will take the path of least resistance. The best way to deal with them in my opinion is through discouragment. There's lots of potential targets for these losers, your best bet is to make yourself a less appealing target. And I do that by playing hardball with them. It's not about revenge or getting them back or even justice. It's purely about finding the lever that makes them go away when a simple ban just doesn't stick.