I'd want to save the name "WTF-8" for that case where someone takes some text encoded as UTF-8, decodes it as if it's in a single-byte encoding, and then encode

I'd want to save the name "WTF-8" for that case where someone takes some text encoded as UTF-8, decodes it as if it's in a single-byte encoding, and then encodes the resulting mojibake as UTF-8 again. Double UTF-8. WTF-8.