On somebody's head be it - Idioms by The Free Dictionary
on somebody's head be it
on (one's) (own) head be it
The blame, consequences, or responsibility of a risky, dangerous, or foolish decision or action belongs to someone and no one else. If she wants to quit a high-paying job to chase after some fantasy of being a travel writer, then on her head be it.
on somebody’s (own) head ˈbe it (often used for warning somebody) somebody is alone responsible for the results of their action or decision: You refuse to go to your own daughter’s wedding? On your head be it! ♢ On his own head be it if he decides to leave college early.