('informal') You need to 'get it into/through your thick skull' [=you need to realize/understand] that you can't just sit there and expect everyone else to do your work for you!
('informal') He can't seem to 'get it through his skull' that I don't like him.
He had a fractured 'skull'.
(..) forgiven for all wrongdoings? JULES: Get the fuck out my face with that shit. The motherfucker said that shit never had to pick up... itty-bitty pieces of skull on account of your dumb ass. VINCENT: I got a threshold, Jules. I got a threshold for the abuse that I will take. (..)1994 Pulp Fiction
(..) is take those cleaning products and clean the inside of the car. I'm talking fast, fast, fast. Go in the back seat... scoop up all those little pieces of brain and skull. Get it out of there. Wipe down the upholstery. Now, it don't need to be spick-and-span. You don't need to eat off it. (..)1994 Pulp Fiction