frighten the hell out of
frighten the hell out of someoneand 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 someone
to 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.
frighten/scare the hell out of somebody(informal)
to make someone feel very frightened He drives like a madman - frightens the hell out of me.