I found it! I found the origin of “the” quoi flag!
This has been a mystery to me for some time now. I’ve known for a long time that Cor was the coiner of quoiromantic (which I discovered via a link in a post by Sciatrix, I think) but when I saw a quoi flag in a compilation of flags, I remember being like “…There’s a flag? …Does Cor know about this?” And no! It turned out! Cor discovered it long after I did, and was never consulted or notified! Which, I think is a little weird, but there we are. Mystery solved.
edit: found some variations/discussion here