Scare the shit out of somebody
Definition 1 of 1
Pro Tip 1/3Very Informal
This phrase is very casual and can be inappropriate in formal or polite situations. 
I'd never use 'scared the shit out of me' in a job interview.
Pro Tip 2/3Intensity
Use it to express an extreme level of fear, more than just being 'scared'. 
When I saw the spider, it scared the shit out of me.
Pro Tip 3/3Not Literal
It's a figure of speech for extreme fear, not to be taken literally. 
Hearing the ghost story around the campfire scared the shit out of me.