Harm a hair on (one's) head phrase
This phrase is often used in the negative.
To harm someone physically to even the slightest degree.
Don't be scared! No one dares to harm a hair on your head in my presence.
He threatened to kill me if I harm a hair on his son's head.
He only harmed a hair on her son's head, but she beat him violently.
Beat someone up
To make one feel extremely upset, hurt or offended
If you do something dangerous or risky, you will get hurt.
The verb "harm" must be conjugated according to its tense.
The origin of this phrase is not clear.
Used to raise caution
Always remember to put safety first whenever you drive.