Ha, I had to look up 418.
418 I'm a teapot (RFC 2324) This code was defined in 1998 as one of the traditional IETF April Fools' jokes, in RFC 2324, Hyper Text Coffee Pot Control Protocol, and is not expected to be implemented by actual HTTP servers.
418 I'm a teapot (RFC 2324) This code was defined in 1998 as one of the traditional IETF April Fools' jokes, in RFC 2324, Hyper Text Coffee Pot Control Protocol, and is not expected to be implemented by actual HTTP servers.
http://http2.github.io/http2-spec/index.html#ErrorCodes
A quick Google shows that it's previously just been used by Twitter to demonstrate rate limiting.