The comment from "English Teacher" is correct. This is an idiom meaning that a person lacks common sense. To understand this idiom, imagine that a person's head is attached to his body like a screw - if his head is "screwed on backwards," then he is facing his backside and therefore, unable to see either what is ahead of him or what he is doing. Example usage: "Even after making a shopping list, he still forgot to buy beef for the stew - it was as though his head was screwed on backwards."

Yes they still use this phrase on occasion. It means they don't know what they are doing!!!

Two similar phrases are "hasn't got a clue" and " he wouldn't know if his house was on fire" Examples: Don't ask Tim to help you. He is so scatterbrained that he hasn't got a clue which door he should open. He wouldn't know if his house was on fire.

哦耶！又学到新东西了。继续关注~~

They still use it. It means someone lacks common sense or behaves in strange ways.