scare the bejesus out of (someone)
To shock or frighten someone very suddenly and/or severely. ("Bejesus," a mild euphemistic oath, is here used as an intensifying noun.) Don't sneak up on me like that, you scared the bejesus out of me! That car accident seems to have scared the bejesus out of Janet—she's still shaken by it.
scare the bejesus out of someone
frighten someone very much. 2001 GQ This place is going to scare the bejesus out of the fuddy-duddy Sloaney-Pony set.
Bejesus is an alteration of the exclamation by Jesus! It is often found in its Anglo-Irish form bejasus or bejabers .