I promise that knowing it’s supposed to be a joke is _not_ going to make you less frustrated if you ever end up having to debug a non-descriptive 418 error. To make it worse the description and the error code aren’t even consistent. 4xx is a client error, but your web server being a teapot is definitely a server side problem.
No, it should be a client error. The error is intended to be returned when a client has asked a teapot to perform a coffeepot-only operation - which is obviously a mistake on the client side.
This makes it similar to 405 Method Not Allowed, 406 Not Acceptable, or 426 Upgrade Required.
Sure, but I’ve actually had to debug a few 418 errors on production workloads, and none of them involved teapot services. Knowing that the implementers of the error thought it was a hilarious joke certainly didn’t make the experience more fun.