How do I stop some big mean missed command from tearing up my main drive?

The answer: Use Ctrl-C. And if that don't work, use more Ctrl-C.

And if that don't work? Use Ctrl-Z.

There are tools like snapper and btrbk that periodically make snapshots. Since btrfs is a COW filesystem, the live subvolume just stores newer changes on top of the snapshot — it doesn't need to copy anything until it changes. Only when file data is no-longer referenced is it actually marked free to overwrite. This can make disk usage a bit un-intuitive since you can have large files stuck in snapshots that don't show up in your live subvolumes but still use up space. It can really save you from serious mess ups and is really cheap in terms of performance. It's also possible to send snapshots over a network to another machine if you want longer term backups without keeping them on local disks.

That was intentional :)

Apart from the initial "Rise and Shine" before the first sentence, this is a direct play on G-man's intro speech from HL2.

when I was but a baby sysadmin, my boss did that to a production server

Hah, fair enough!

after mistakenly creating a directory caller ~…

How do you even delete such a directory?

This is why i find rmdir useful.