scare the pants off
Verb
Meaning
scare the pants off (third-person singular simple present scares the pants off, present participle scaring the pants off, simple past and past participle scared the pants off)
(slang, idiomatic) To scare or startle someone thoroughly.
He liked the water rides, but the big roller-coaster scared the pants off him.
Synonyms
spook
frighten
terrorize
terrify
affright
petrify
scare the bejeebers out of
scare someone's pants off