I didn't know 418 and I'm a web dev. Http status codes are a tiny part of my job
I think the appropriate action would be a client sends an HTTP HEAD to the service, which responds 200 "TEAPOT".
http://fellowproducts.com/shop/staggekg/
I have the plain EKG, and quite like it.
However, both are designed for pour-over coffee, so can’t correctly return 418.