Achilles' heel

A person's weak spot is their Achilles' heel.

Adam's apple

The Adam's apple is a bulge in the throat, mostly seen in men.

Any Tom, Dick or Harry

If something could be done by any Tom, Dick or Harry, it could be done by absolutely anyone.

Barkus is willing

This idiom means that someone is willing to get married.

Before you can say Jack Robinson

The term Jack Robinson represents 'a short amount of time'. When you do something before you can say Jack Robinson, you do it very quickly.

Benjamin of the family

The Benjamin of the family is the youngest child.

Buggles' turn

(UK)

If it Buggles' turn, someone gets promotion through length of service rather than ability, especially in the British civil service.

Davey Jones' locker

Davey Jones' locker is the bottom of the sea or resting place of drowned sailors.
('Davy Jones' locker' is an alternative spelling.)

Do a Lord Lucan

(UK)

If someone disappears without a trace or runs off, they do a Lord Lucan.  (Lord Lucan disappeared after a murder)

Even Stevens

If everything is equal between people, they are even Stevens.

Every Tom, Dick and Harry

If every Tom, Dick and Harry knows about something, then it is common knowledge.

For Pete's sake

This is used as an exclamation to show exasperation or irritation.

For the love of Pete

Usually used in exasperation, as in 'Oh, for the love of Pete!'

Freudian Slip

If someone makes a Freudian slip, they accidentally use the wrong word, but in doing so reveal what they are really thinking rather than what they think the other person wants to hear.

Going Jesse

(USA) If something is a going Jesse, it's a viable, successful project or enterprise.

Great Scott

An exclamation of surprise.

Hobson's choice

A Hobson's choice is something that appears to be a free choice, but is really no choice as there is no genuine alternative.

Home, James

(UK) This is a cliched way of telling the driver of a vehicle to start driving. It is supposed to be an order to a chauffeur (a privately employed driver).  The full phrase is 'Home, James, and don't spare the horses'.

In like Flynn

Refers to Errol Flynn's popularity with women in the 40's. His ability to attract women was well known throughout the world.  ('In like flint' is also used.)

Is Saul also among the prophets?

It's a biblical idiom used when somebody known for something bad appears all of a sudden to be doing something very good.

Jack the Lad

A confident and not very serious young man who behaves as he wants to without thinking about other people is a Jack the Lad.