"Now and then" means that something occurs once in a while. If someone asks, "does it rain here," and it only rains a few times a year, you could say "now and then it rains." This is used to indicate something that doesn't happen often.
"Now and again" is the same as once in awhile.
i don't now
It means "sit down" in idiom slang. The original phrase was "pop a squat", the word "cop" is a dialect misunderstanding, but now both pop and cop are used in the idiom.
RFP is not an idiom. It's an abbreviation.
It's not really an idiom. It means "what are you thinking about."
It is not an idiom, it means your nose is itching.
idiom means expression like a page in a book
It's not an idiom. It means the tip of your nostril.
"Sieve" is not an idiom. See the related link.
This is not an idiom. It is a measurement. $100,000 is how you write it in numbers.
Simply its mean a bully.
The idiom your blood is boiling usually means that you are mad/furious.