418
I’m a teapot
This resource is short, stout, and permanently a teapot. It will not brew coffee, not today, not for you, not for anyone.
HTTP/1.1 418 I'm a teapot Safe-to-brew: true (tea only) Accept-Additions: milk, sugar, sympathy Retry-After: heat-death of the universe
Per HTCPCP, RFC 2324 §2.3.2. The status code is real. The teapot is real. The coffee is not.