Like accidentally mounting your root subvolume in your home directory while it's still mounted as root. I mounted root to a directory called games in my home folder. I noticed some crap in it after accidently copying the contents of the wrong directory into it and without a second though rm -rf games/* Before I knew it, I saw my desktop unload before my eyes until I was left with nothing but a solid white _ in the top corner.

My home folder was on a slow hard drive and I was trying to make a subvolume on the small but fast SSD. I ended up just making a symbolic link to a folder on root after reinstalling.