From experience it seems that the best way to avoid conflict is to quickly ban anyone who demands a CoC

I thought so too at one point, but now I'm skeptical. The demanders will keep filtering in, and random people unacquainted with past stories of CoC abuse may feel uneasy.

So I think the best way is to: be a BDFL, proactively have a CoC that reflects your values (and to hell with any standard formulations), and make it explicit up front that anyone who wants changes to the CoC can go kick rocks (or, you know, fork the project). And that they're welcome to do so, and won't be interfered with outside of the project's own spaces.

And people who don't like an existing BDFL, rather than trying to take over or start drama in project discussion spaces, should just fork ASAP.

It's also easier for a small, closed group to keep their conflicts private.