Bore, scare, etc. the pants off somebody British American spoken language informal
To make someone feel extremely bored, annoyed, frightened, etc.
The investigation frighten the pants off the board of directors.
The sound of the fire alarm system scared the pants off everyone living in the building this morning.
The verb "bore/scare" should be conjugated according to its tense.
There is no clear information about the origin of this expression.