So what are your guild's unwritten rules? I find that they usually revolve around people-- someone does something that gets them remembered, and then everyone knows the joke after that. Guildleaders tend to set a lot of the unwritten rules as well, since they're there at most of the raids anyway. And some of the rules just plain have to do with etiquette-- who belongs in group 1, who explains which fights, who runs the tasks of main looter and calls boss phases.
None of this stuff is programmed into the game, obviously, but of all the hundreds (and thousands) of guilds out there, each one, I'd bet, does things their own way.