I don't believe "official" Guidelines need to be established, I think if we start to establish what is "okay" to RP we start down a path where we severely limit players in what they can and can't RP. I personally find realms far more fun when there is active RP going on. I think if we start to establish rules around what can and can't be put into a RP then we start to dump sand and dirt on the fire and passion for RPing that some players have.
I don't at all agree with your opinion that the cited RP was over the line and graphic. It was, I think, ambiguous to the point that a child (Someone say under the age of 10 or 11) wouldn't really get/understand what was implied to have happened next.. I.e. the rape and/or murder of the peasant.
I hope I don't come off as condescending here, but I think if the RP was truly graphic and over the top, more people would have stepped forward and said something, myself included. I am not advocating for allowing players to brutally and graphically describe rape in game, but I don't think players should be limited by official guidelines around what is acceptable or not.
I am of the mind that if someone crosses the "line" then they will be reprimanded and action can be taken accordingly. (No idea what that would be). I think it was mentioned before, but if you find that a player or players are continually RPing things that you would rather not see, the ignore feature is there for that purpose..
