As someone who's been on forums of every stripe since the goddamn 80s, I can say with a great deal of experience that all good internet communities have just one single rule: "Don't make us ban you."

Anything else just invites edgy trolls and rules-lawyering.

Now don't get me wrong, guidelines are good and necessary. Give people an idea of the kinds of thing you do and don't want to see, and the way you will generally act in turn, because managing expectations is important.

But the moment you make hard-and-fast rules that you're obliged to follow, people will make a point of bending you over them with edge cases and not cuddling afterwards, just because they can. They think denial-of-service attacks are just as hilarious against human systems as they are against software ones, if not moreso - or they do it to assert control as part of one personality disorder or another.

If you play their game, you will lose.

You need to have an admin-discretion clause, and not feel bad about invoking it whenever it's the right thing to do.

Of course, this can lead to tyrannical asshole mods - if you have a mod team, you need to keep a close eye on it to prevent shitty personalities taking over in that domain. As the person that the buck stops with, if you can't trust yourself with it, then the place is going to hell anyway.