I've never understood the term (used quite often in threatening way by my father when we kids were being ornery) "If you don't stop now, I'm gonna crease your skull."

To me it was nonsensical because a skull is not fold-able? Did he mean he would iron our heads? How silly! Or was it, since my mom had told me she used an iron to straighten her hair in college?

Has anyone else heard term "crease your skull" or near variation?