It goes in one ear and out the other?
forget immediately (usually because you're not listening well or don't care to)
I can't seem to wrap my head around it
having trouble understanding
The ring cost an arm and a leg
it is very expensive
You can't judge a book by its cover
cannot judge something based on its appearance
Feel a bit under the weather
feeling slightly sick
Let the cat out of the bag
to share information that was a secret
Once in a blue moon
rarely happens
Take with a grain of salt
don't take it too seriously
The whole nine yards
includes everything it possibly can
Steal someone's thunder
take credit for something they did and not you
He is on the ball
to understand the situation/topic well; be alert
It takes two to tango
something that involves 2 people, typically in a negative connotation (like arguing, for which both parties are responsible)
Best thing since sliced bread
a good idea, invention or plan
At the drop of a hat
do something instantly without hesitation
Ball is in your court
it is up to you to make the next decision/step
He has bigger fish to fry
he has more important things to take care
