This is an anti-pattern. A better, future-proof solution would be to extend HTTP 418 with a header stating just what the server is not:
HTTP 418 I'm A Teapot
I'm-Not-A: freezer;teapot;radioThis is a proposal to add a new HTTP status code. 418 is not a HTTP status code but a HTCPCP status code.
needs more dry; just remove the second I'm and it's clearer.
Should be "I'm a little teapot" short and stout is implied
421 Misdirected Request works equally well.
Considering 418 is the positive assertion, suddenly reversing that would break backwards compatibility; additionally, it adds ambiguity by listing multiple entities it is not, leaving the receiver to potentially assume that it is, for example, a microwave.
EDIT: missed the positive part remaining, sorry. I maintain that the ambiguity issue stands.