418 I'm a teapot
The teapot that refuses to brew coffee — the 1998 joke that became heritage.
RFC 2324, published on April 1, 1998, specifies HTCPCP — the coffee pot control protocol. In it, a teapot asked to brew coffee answers 418, because it is short and stout, as in the song.
In 2017, when someone proposed scrubbing the number from the platforms, the save418.com campaign won: Node, Go and company kept it, and today RFC 9110 marks 418 as (Unused) — reserved, so the joke cannot be overwritten. Visit google.com/teapot and it still answers.
HTTP/1.1 418 I'm a teapot
Content-Type: text/plain
Server: HTCPCP/1.0
short and stout