418 I'm a teapot - Client Error Response Status Code
Example Use
Originated as an April Fool's Day joke in 1998, this response is used for light humor.
The joke states a 418 response should be returned by teapots requested to brew coffee.
The entire parody spec is RFC 7231. This was removed From the latest spec.
Official Definition
Any attempt to brew coffee with a teapot should result in the error code "418 I'm a teapot". The resulting entity body MAY be short and stout.
Source: RFC 7231 Section 2.3.2