Ah, that magical moment when evening-wear and onesies collide!
We're most confused by the tweed fabric used in this. When would you wear a tweed "onesie"? In some other fabric, and if, say, it had a skirt, rather than what appear to be cycling shorts at the bottom, it could just've worked - or at least been a whole lot less puzzling.
Of course, that would defeat the whole purpose of the tweed onesie, though, and Alexander Wang wouldn't be able to charge $395 for it. Ah, fashion!