![Smile :)](./images/smilies/icon_e_smile.gif)
I'm not saying there's no need for a way to try to deal with griefers; just saying that I don't think that you can define a set of actual systems that dictate what constitutes "reportable" behaviour. A way to share information about which players have behaved badly (for whatever the server they're on's definition of "badly") in a more structured and automatic way than a forum thread would be neat, I'm just not sure there's a way to prevent that system itself from being abused, and you just have to come up with something robust enough that it'll be rare.
I don't know how the account verification system in Factorio currently works, and it's very likely that it *doesn't* currently work in a way that would permit this, but it's possible in principle to have a system such that one game server can prove to a third party (cryptographically) that a given player was actually connected to the server, in an unspoofable way, if it had the central authentication server's help. If that was available, then you could use that to build a system that could tell you how many servers a player has been banned from, and use that to evaluate whether you want them to connect or not. If you connected to a server run by mean people, they could indeed ban you and get you a single "black mark", but they wouldn't be able to report you over and over unless you connected to a bunch of other servers run by the same people. It could still be up to every individual server what the standard/systems are for you to get banned, and how many servers you have to have been banned from for the server to not let you on in the first place.