Hum, I don't think there are rules about that. As per unwritten rule we do not accept pornography, since that does not belong to the movie nor is it suitable for the younger audience on this forum. Anything else would be okay, in my opinion.
However, if readers are disgusted or angry about something that's written in here and mention this to the admin team, we might look into it and send the author a PM regarding the removal of the topic.
PG rated is fine.