Bore, scare, etc. the pants off somebody
Definition 1 of 1
Pro Tip 1/3Colloquial
Used in casual conversation, not in formal situations like business meetings or academic papers. 
His pranks are legendary; they scare the pants off everyone.
Pro Tip 2/3Hyperbole
It's an exaggerated expression, not meant to be taken literally. Nobody's pants are actually removed. 
You jump so high! You could scare the pants off an NBA player!
Pro Tip 3/3Figurative
Illustrates an extreme effect, either frightening someone a lot or making something unbearably dull. 
That haunted house will scare the pants off you!