You can just say that there should be no personal attacks, people should be civil to each other, and nothing that a reasonable person would construe as racism o

You can just say that there should be no personal attacks, people should be civil to each other, and nothing that a reasonable person would construe as racism or harassment. This is similar to the rules on wikipedia, and it works very well there. The problem is that there is a small minority of people who don't/can't see things from other people's perspectives, so they either make blatantly offensive comments without realising it, or they get offended and their feelings hurt when no reasonable person would have taken a comment to be offensive. Perhaps there could be a peer-based mediation panel within Google to make non-binding, non-public rulings on these cases without them going to HR (if both parties agree on the outcome). If these panels were make up of reasonable people (think wikipedia admins), then it might work quite well.