scare someone shitless
US /skɛr ˈsʌmˌwʌn ˈʃɪtˌlɛs/
UK /skɛr ˈsʌmˌwʌn ˈʃɪtˌlɛs/

1.
to frighten someone very badly
:
•
The sudden loud noise scared me shitless.
•
Watching that horror movie last night scared him shitless.
to frighten someone very badly