system
A chat on subreddit /r/pcmasterrace
human
If this is the wrong subreddit to post this question, does anywhere know which subreddit this is appropriate on?
gpt
Possibly some subreddit related to tech support or Linux/UNIX systems.

For a possible solution: 
I would recommend trying to just delete all partitions on the drive and then attempting to install Windows again. (Assuming there's no partitions on there that you need.) This would guarantee that the partition with the GRUB bootloader would definitely be gone.