Wiktionary
scare the pants off
vb. (context idiomatic English) To scare or startle thoroughly.
Usage examples of "scare the pants off".
The demon made all the papers, morphing into all sorts of figures to scare the pants off everyone in the courtroom.
If it disintegrates a single village that'll sure be enough to scare the pants off every citizen in Europe.
By the time I got home I'd know how to tell Carla the truth in a way that wouldn't scare the pants off her.
We're going to jump to the shore and scare the pants off a Mounder!
One way of spurring departures is to scare the pants off people, but that's the job of the media, not government.
He could give a cold reading that would scare the pants off a marble statue.