418 I'm a teapot
Meaning
A playful and non-standard status code indicating that the server refuses to brew coffee because it is permanently a teapot. Defined as an April Fools' joke in RFC 2324.
When to Use
Traditionally not used in real applications except as an Easter egg. Some services might use it humorously or to indicate a request was blocked in a whimsical way.
Example
Sending a request to a coffee-brewing API endpoint on a teapot might return 418 I'm a teapot as a joke response. For example, some websites return 418 as an Easter egg for teapot-related requests.
When Not to Use
Do not use for serious purposes. This code is not meant for real HTTP operations. Use standard 4xx or 5xx codes for actual errors instead of 418.
Source
RFC 2324 (April Fools)