Error Code 418: I'm a teapot.
Started as an April Fools' Joke in 1998, status code 418 is real and sometimes used to handle responses that the web server doesn't want to deal with. The official docs state:
2.3.2 418 I'm a teapot
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