I’m sure the anti-NPM brigade is on its way, but I recall there being a huge backlash against removing this error code from Node a few years ago.
Heck, technically the problem isn't even that it's used by the registry, the problem is the npm client is a broken untestable mess and users seem to routinely unearth extremely surprising bugs.
This all has very little to do with teapots. The fact they used 418 and didn't provide a useful error message only makes it more interesting to talk about.