Whenever you see an idiom stating that something is "a different _______" (a different kettle of fish, a horse of a different color, etc), it just means that whatever topic has just been mentioned is totally different from what was spoken before. For example, if the topic of conversation is gambling, and someone mentions the game of bingo, a person might say "That's a whole different kettle of fish -- bingo isn't really gambling at all."
"To be" is not an idiom - it's a verb.
Pest is not an idiom. It's a word.
The idiom "apple shiner" means the teacher's pet.
The meaning of the idiom in the pink of health means being in good health.
Smoking pipe that uses water to filter smoke.
Criticism from someone who is just as bad.
Whenever you see an idiom stating that something is "a different _______" (a different kettle of fish, a horse of a different color, etc), it just means that whatever topic has just been mentioned is totally different from what was spoken before. For example, if the topic of conversation is gambling, and someone mentions the game of bingo, a person might say "That's a whole different kettle of fish -- bingo isn't really gambling at all."
"To be" is not an idiom - it's a verb.
That's a pot calling the kettle black.
Pest is not an idiom. It's a word.
The idiom "apple shiner" means the teacher's pet.
The meaning of the idiom in the pink of health means being in good health.
It's not an idiom - to cope means to deal with, or to handle
The idiom means impress someone is egg on
"Old hand" is an idiom meaning having lots of experience.
It is not an idiom. It is an expression. The difference is that an idiom's meaning cannot be derived from the meaning of its individual words. In the expression wolfing down food, the meaning is clearly derived from the meaning of the words, and people have been saying it for hundreds of years.