On (one's) (own) head be it spoken informal
Used to alert or remind someone about their plans or actions which they will have to be held accountable for.
My father said that it is the job that you had chosen and on your own head be it.
If you insist that you can go alone without us, on your head be it.
On his own head be it if he decides to leave the company.
To stay calm in a difficult situation and react to unexpected things quickly
Used to warn readers that an important detail of the plot is about to be revealed
To keep an eye on your enemies' behavior in order to avoid any malicious actions
Used when you want to warn someone that he or she will be in danger or that something bad will happen to them
If someone or something keeps one on one's toes, they force him or her to stay active and focused.
A source said that the phrase has been used in the sense "Of a misfortune, curse, blessing, etc.: directed towards a person; so as to affect a person; on a person" since Old English.
To be very wet
Because of forgetting bringing an umbrella, I look like a drowned rat when it rains.