The Ruby project discusses adopting the Contributor Covenant

As usual, nobody advocating a CoC can point to any situation in the project's history where having a CoC would have improved the situation. There's also a few classic kafkatraps in the discussion ("your opposition to my proposal is just proof that my proposal is required.") All it'll need is to wrap up with some high-level authority ramming the code of conduct down the community's throat to be a classic example of how these discussions usually go.