[ale42]

I started reading RFCs as a teenager when I stumbled upon an RFC collection on a CD-ROM distributed with a computer magazine. It didn't last long until I started implementing my own SMTP client.

And then I discovered this, and for a moment I was a bit afraid: TELNET SUBLIMINAL-MESSAGE Option [https://www.rfc-editor.org/rfc/rfc1097.html]. I didn't immediately understand it was a 1st April's joke, and was thinking something like "how many other weird things nobody ever heard about are actually implemented into Internet software?". Also because, of course, I was regularly using Telnet at that time. Then I realized the date and the fact that the option number (which is supposed to be a byte) was defined as... 257. Later I discovered that of course 256 was already assigned to the Telnet Randomly-Lose option, the very first such RFC, a comment of which seems very contemporary despite having been written in 1978: "Several hosts appear to provide random lossage, such as system crashes, lost data, incorrectly functioning programs, etc., as part of their services.".

The whole collection is here: https://en.wikipedia.org/wiki/April_Fools'_Day_Request_for_C.... And as other people mentioned, some are really funny.