I think an unofficial behavior code definitely already exists. Everyone agrees, pretty much, that spamming messages of any type is annoying, and things like asking for the admin pass get old really fast. Even if we were to create something more formal, many people simply wouldn't care or would think that when they yell "AIR! 3HK! YOU CHEAT!" it's not spam because it actually was an air 3hk. Plus, the only thing you could do to enforce a set of rules would be to mute/kick/ban offending players. Which is exactly what is already done to players who violate the informal rules.

So, while having a set of rules to govern behavior online does make some sense, I think that trying to implement it would just lead to some massive flamewar over exactly what the rules should be, and would have minimal effect on actual online behavior.