frighten the life out of someone

frighten the life out of (one)

To shock or frighten one very suddenly and/or severely. (Hyperbolically alludes to frightening someone so severely as to cause them to die.) Don't sneak up on me like that, you frightened the life out of me! That car accident seems to have frightened the life out of Janet—she's still shaken by it.
See also: frighten, life, of, out
Farlex Dictionary of Idioms.

frighten the life out of someone

or

scare the life out of someone

INFORMAL
If someone or something frightens the life out of you or scares the life out of you, they frighten you very much. It used to frighten the life out of me when they tried to jump on the moving trains. Further tests revealed that I needed major heart surgery. It scared the life out of me.
See also: frighten, life, of, out, someone
Collins COBUILD Idioms Dictionary, 3rd ed.
See also:
  • frighten the life out of
  • frighten the life out of (one)
  • frighten/scare the life out of somebody
  • frighten the hell out of
  • frighten the hell out of (one)
  • scare the (living) daylights out of (one)
  • scare the living daylights out of someone
  • frighten the (living) daylights out of (someone)
  • frighten the daylights out of
  • frighten the pants off (of) (one)