('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'.
(..) They done it. They took their sweet () With it too at the start I didn't feel nothing, I just heard the sound of... ...knife scraping against my skull, you know ... They were all laughin' and whoopin' and hollerin' what not... Then the blood came ... The cold started streaming down (..)2015 The Revenant