https://www.theregister.co.uk/2018/05/29/npm_teapot/

npm, the widely used and defiantly lower-case Node.js package manager, on Monday briefly returned an error to users connecting to the registry via proxy who attempted the npm install command.

The error message declared "npm ERR! 418 I'm a teapot…", in reference to a RFC 2324, a tongue-in-cheek coffee pot communications protocol created as an April Fool's joke in 1998.