Is it a dress? Or a giant tube sock?!
It's actually a chunky mohair tube scarf by the Bulgarian knitwear brand Dukyana. You just slide inside of it.
It's 8 feet long and there are no holes for your arms, so you can just relax because you can't do anything else.
There's probably enough room inside for snacks if you have them when you put it on.
I can be yours for $280.