[rwbcxrz]

To answer your question, probably Gamergate.

In an article about maintaining an open source project, it seems to me like covering contribution guidelines (which I would consider a CoC to be part of) is pretty important.

In my experience, many projects maintain codes of conduct not because they've had frequent problems, but as a statement that the maintainers welcome contributors from all backgrounds, skill/experience levels, etc., and that they won't tolerate behavior that alienates others.

Regardless, every project has some sort of CoC, even if it is never explicitly stated. Putting it in writing makes it clear to everyone (including the maintainers), and that seems like a good thing to me.