Knowing software developers, probably entirely serious.

The seasoned sysadmins are a little more careful before smacking the enter key...

Depends on the importance of the system. If it's a fairly unimportant home system that's excessively backed up, it's fairly easy to live life on the edge.

rm -i and rm -f (as well as mv and cp) allow to specify certainty not merely for everyone above UID 0.

Keyword: Backups.

It’s probably just a shell script or an alias

An alias would work but it wouldn't say rebnooting. That was my initial fix. But I was learning things at the time and I learned how to recompile parts of the distribution. I also learned how programs in Unix could invoke different effects based on name. Coming from DOS, it was a real surprise that reboot was a link to shutdown.

So I am assuming you ended up patching the `shutdown` binary to print `Rebnooting` if exec'd with the `rebnoot` name?

This is similar to how busybox binary implements a bunch of the tools from coreutils etc.