What do you mean by working overtime and screwing around?

Working overtime with screws is actually working overtime. Working with screws has now become a mockery of work, intended to show that you have become an overtime machine.

Screwing is the lowest job in the factory, and when people say that you should go to the factory to screw, it means that your current job is too bad and you are incompetent at all.

Of course, the meaning of this sentence is mostly ridicule, and there is not much malice. It can be used as a kind of ridicule between friends, and everyone can laugh it off.