If a person is "hard of hearing" it means they find it hard to hear things, they either have a congenital hearing problem or for some reason (eg age, disease or industrial injury) they are going deaf.
To be "hard of hearing" means that you are somewhat deaf.
To complain or criticise someone out of their hearing.
It's really not an idiom. It means just what it seems to mean -- someone finds it hard to hear. They are either partially or fully deaf.
Life Is Sometimes Hard
The idiom "a nut to crack" has the basic meaning of "a problem to solve." Some "nuts" are hard to "crack," while others are easy, but this can only be determined by context.
"To be" is not an idiom - it's a verb.
The meaning of the idiom "to slap the back off you" is fairly straightforward. It implies an exaggeration, that one would slap someone else so hard that their back would come off.
Pest is not an idiom. It's a word.
Perhaps you mean "crack you up." This is an idiom meaning to make you laugh a lot. The image is of you laughing so hard that you crack apart.
That would be "crack you up" - the image is of you laughing so hard that your sides crack open.
The idiom "apple shiner" means the teacher's pet.
The meaning of the idiom in the pink of health means being in good health.
my grandfather is a bit hard of hearing