If there was one ethical rule that I could mandate for all it would be not talking behind someone else's back. In other words, if you have someone to say about someone it should be to them. This is seems like a perfectly good ethical rule to follow until you think through its consequences....
I was actually in a work environment - it was a bit of an experiment - where "triangulation" (speaking of others who are not present) was disallowed. I thought this was a fabulous rule until I realized that I needed to speak to others about certain situations in order to validate my experience, to talk through it in order to understand it.
I now understand that this is sometimes what people are doing when they speak 'behind the backs' of others, and that it is not necessarily malicious even if it can have negative consequences. Being able to check in with others about our experiences is especially necessary for the under-represented or disenfranchised because their experiences and realities are so often denied, obfuscated, or disparaged.
What this taught me is that ultimately there can be no absolute ethical laws - this is just one example to illustrate the belief. We have to use our human judgement and empathy to determine how to act in any given situation. It is up to us to decide how to act and any rules can only serve as general guidelines from which we may begin our deliberations.
I try not to speak of others behind their backs, and I certainly try not to do so in a malicious way, but I also know that sometimes I will need to do this, and sometimes I will need to allow others to do this, as a normal part of the processing that we need to do with each other.
So I guess that I don't believe there can be any static laws where it comes to humans.