Chat rooms can have very different policies and cultures, which leads to issues due to the global nature of the flagging system. One example that regularly causes confusion and drama is the question whether profanity is allowed in chat or not. Many chat rooms have a very informal atmosphere, and a bit of profanity (or even much more) doesn't tend to be a problem. But that isn't the case for all chat rooms.
Users that just entered a room or users that see a flag in a room they're not familiar with have no easy way to find the rules of a particular chat room. What I propose is a moderator-editable field for each chat that contains the rules the chat room community has agreed on. I'm thinking of a very short list, something like no more than 3-4 bullet points, not an epic essay. Just the most important stuff that isn't already in the SE code of conduct, e.g. "we curse like drunken sailors in here".
This short list of rules would be linked from the chat sidebar, so that new users could find it there. It would also be shown to flaggers along with the actual flag, so that they can quickly see the particular rules that apply in the room.
This is of course no license to do whatever you want in your chat room, the SE code of conduct and the terms of service still apply. So you can't make a room where insulting other users is acceptable, or a room for posting porn or something like that.