'Error 418: I'm a teapot' scores 'reserved' status in IANA Status Code Registry
From what feels like the Internet Dark Ages of the 1990s, was the Hyper Text Coffee Pot Control Protocol, a joking anticipation of the Internet of Things, which gave the world HTTP Error 418:
Story at the Register https://www.theregister.co.uk/2017/08/14/error_418_im_a_teapot_preserved/
That wonderful April Fools Error 418 - https://www.google.com/teapot
(click the teapot)
The April 1st, 1998, Internet Working Groups spec on
"Hyper Text Coffee Pot Control Protocol (HTCPCP/1.0)"