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.
See also: head, on

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.
See also: head, on