Guys not be the one who breaks up the laugh fest but that bird has hit it's head and has brain damage or it has encephalitis. examine it's head for wounds. Has anything scared them and caused them to flush lately?
Sometimes it's just caused by cranial swelling that will recede. Most often you will need to euthanize the bird.
Doubtful that it is encephalitis, unless they have had access to moldy food.
Separate it and give it a couple days to heal if you'd like, and it seems humane. There is a small chance it will heal.