My language partner asked for help with American Idioms. Specifically, what is really used today? I found a site with many, many idioms but many of them I never hear today. But using this site (listed below) I called out which ones I feel are common today and where used (business, casual, formal...). Below are the 'A' idioms.

Is this interesting to anyone? Should I keep posting other letters? Comment or message me, thanks.

About time:
Nearly time, high time. ex. "It's about time you bought a new car!"
Used quite often, but it is considered very sarcastic. Use with friends.
COMMON

Absence makes the heart grow fonder:
Proverb that means that our feeling for those we love increases when we are apart from them.
Everyone understands, but is rather formal. Not used very often in every-day speech.

(To) act high and mighty:
To act proudly and arrogantly. ex. "He has been acting all high and mighty ever since he chased away that burglar."
Is used in casual conversation, but is also very sarcastic.

Actions speak louder than words:
Proverb meaning that's it's better to do something about a problem than to talk about it.
Is used, but is rather critical of someone. But it is a subtle way to tell someone it is time to get to work.

(To) act one's age:
To behave in a more mature way. Frequently said to a child or teen. ex. "Bill, stop throwing rocks! Act your age!"
Not used very often, is a little bit formal. The example above is one place where parents would use.

(To) add fuel to the fire:
To make a bad problem even worse. ex. "He added fuel to the fire by bringing up old grudges while they were arguing."
Common and OK to use. Often said in the negative, "Not to add fuel to that fire, but..."

(To) add insult to injury:
To make a bad situation even worse.
Common and OK. "Getting a snow storm on the day you are already late for work just adds insult to injury."

Against the clock:
To attempt to do something "against the clock" is to attempt to do something as fast as possible, usually in order to make a deadline. ex. "They were working against the clock to finish the project."
OK to use, but a little old-fashioned.

All out (adj./adv.):
Full-scale; complete. ex: "They said it was only a few skirmishes, but it was an all-out war."
Another common use, "We're going all-out to get the project finished this week."
COMMON

All set:
Ready (to go). ex. "All set?"
Very common.
COMMON

All thumbs:
Awkward. Clumsy.
Very old-fashioned.

A little bird told me:
When someone says "a little bird told me", it means they don't want you to know who told them.
Not used very much anymore.

All in a day's work:
Typical; normal; par for the course. ex. "Talking to famous celebrities is all in a day's work for some Hollywood reporters."
Used sometimes, but a little old.

(From) all walks of life:
(From) all social, economic, and ethnic groups. ex. "People from all walks of life voted for him, but he still lost the presidential election."
Not often used.

Apple of someone's eye:
Someone's favorite person (and sometimes thing). ex. "Sarah was the apple of Tom's eye for quite a long time. He was very much in love with her."
Very old saying. My grandmother may have said this.

Armed to the teeth:
Heavily armed. ex. "The rebels were armed to the teeth."
Not said very often.

At all hours (of the night):
Very late at night, throughout the night. ex. "Her boyfriend would call her at all hours of the night."
Commonly used.

At each other's throats:
Fighting or arguing hard. ex. "They were at each other's throats. The arguments never stopped."
Not commonly used.

At this stage:
At this point. ex. "At this stage, it's difficult to say who will win the election."
Very common to use in a sentence like above example.
COMMON