(as) black as (one's) hat old-fashioned simile
Completely black; totally dark
This place looks so creepy, it's as black as my hat!
I can't see anything in this tunnel, it's as black as my hat.
Completely dark, without any light or color
Completely black, without any light or other color
Completely dark
People tend to like forbidden or illegal things just because they are forbidden or illegal.
He must have believed that stolen fruit is the sweetest, and he, therefore, cheated on his partner.