The way I like to do things, is make the rule very clearly good-natured.

Something along the lines of “be nice” or “don’t be a dick”. Very broad, but really just a kinder way to say “use your common sense” and “don’t piss me off”.

The particular rule should almost never be cited in favor of clearer rules when applicable, but it gives you an out when you need to take action to deal with someone who is being difficult.

I also think it signals to people that your rules represent an ideal, rather than just their literal meaning. That people should read between the lines a little, in order to judge what will and won’t fly. Basically, making it a “don’t violate the overrall spirit of the rules” clause.

As an example, “no cringe” is a rule on my northstar game servers. Once, I cited it when banning a trio of players who’d log onto one of my servers, and then hog it by votekicking anyone who joined afterwards. This prevented other players from joining, as they could never outnumber them by enough to no longer make 3 votes a majority.

They didn’t break some explicit rule, but I host my servers for all to use. If they wanted to have a private game, they could do the same. My servers weren’t theirs to hog, and they stopped dozens of others who wanted to get a larger game going from doing so.