frighten the hell out of (one)
To shock or frighten one very suddenly and/or severely. Don't sneak up on me like that, you frightened the hell out of me! That car accident seems to have frightened the hell out of Janet—she's still shaken by it.
frighten the hell out of someone
and frighten the pants off someone; frighten the living daylights out of someone; scare the living daylights out of someone; scare the shit out of someone; scare the wits out of someoneto frighten someone badly, suddenly or both. (Use of hell and shit are crude.) These figures frighten the hell out of me. The door blew shut and scared the shit out of me. It takes a lot to scare the pants off a hardened criminal.