To give Mr. Kim money is like carrying coals to Newcastle because he is already so rich he doesn’t need any more money.

2) Crossing the Rubicon: to pass a point of no return
Example:
Abigail will have crossed the Rubicon when she sends the college application.

3) Rome was not built in a day: great things cannot be done instantly, they take time and patience.
Example:
A: ‘It feels like he’s spent all of his live writing the book.’
B: ‘well, Rome wasn’t built in a day.’

4) New York minute: something that happened in very short time
Example:
She gets all the jobs done in a New York minute, what a fast learner she is!

5) Cut the Gordian knot: to solve a very complex problem in a simple way
Example:
She cut the Gordian knot off the difficult equation.

6) Himalayan blunder: a very serious mistake or error.
Example:
He got a warned for his Himalayan blunder.