'a pipe dream'

A pipe dream is a plan or a dream for the future that could never come true or be achieved.

The idea of a perfect world in which everyone lives in peace and harmony is just a pipe dream. 

Pipe dreams only ever come true in the movies.

Origin: Metaphorical, and probably related to the fact that the drug opium can be smoked in a pipe, and when it is taken people often have very pleasant, dream-like experiences.

"kick the habit "

If you kick the habit, you manage to stop doing something that has become a bad habit.

I wish I could stop smoking cigarettes but I just can't kick the habit.

Rashid used to bite his fingernails but his girlfriend made him kick the habit.

Note: "Kick a habit" can be used when talking about habits in general, as in "Kicking a habit isn't easy."

"earn your stripes"

If you earn your stripes, you do something to prove that you have the skills or ability for a particular job or rank.

He earned his stripes in the department of foreign affairs before becoming one of our ambassadors.

You'll need to earn your stripes as a travelling salesman before we can think about giving you more responsibility.

"eat up"

eat someone up
1. . Lit. to consume the flesh of someone. The big bad wolf said he was going to eat you up! The bear ate up the fish.
2. Fig. [for an idea] to consume a person. The whole idea of visiting Australia was just eating her up. The obsession to own a car was eating up my brother and his friends.
3. Fig. [for insects] to bite a person all over. These mosquitoes are just eating me up! The bugs literally ate up all the hikers.
4. Fig. [for someone] to overwhelm and devastate someone. The guy is a devil! He just eats up people! Fred will just eat you up. He is a vicious administrator.

eat something up
1. . and eat an animal up Lit. to devour all of some food or an animal. They ate the turkey up, and no one had to eat leftovers. The lion ate up the zebra very quickly.
2. Fig. to consume something rapidly, such as money. Running this household eats my income up. The car really eats up gas.
3. Fig. to believe something. Those people really eat that stuff up about tax reduction. They'll eat up almost anything you tell them.
4. Fig. to appreciate something. The audience liked my singing; they really ate it up. The stuff about the federal budget went over well. They really ate up the whole story.

"try out"

     David Beckham has been a soccer star for so long, it’s hard to imagine him trying out for his first team. But everyone has to start somewhere, and if you want to prove yourself, you have to try out.

     Sports teams, plays, and bands all require you to try out for a position or role. You have to demonstrate your talent and show that you are a good fit. When you try out, you do a small performance, showing off your best work.

     Beckham now has children who are old enough to try out for soccer teams just like he did when he was little. He says there is a lot of pressure on his kids to do well at team tryouts. People expect them to play just like their dad, even though they are still just kids. Maybe it would be better if they tried out for swimming or basketball instead.

     What have you tried out for in the past? Did you make it? 

“My brother and I both tried out for the debate team, but only I earned a position.”

“Will you try out for the basketball team with me?”

“I would love to be in my school’s play, but I’m too nervous to try out.”

"go out on a limb"

If you go out on a limb, you put yourself in a risky position in order to support someone or something.

He knew it could damage his career, but Keith went out on a limb and said he supported the anti-war protesters.

I don't think that saying you support gay rights means you're going out on a limb these days.

Origin: Probably metaphorical, from the fact that if you're climbing a tree and you go too far out on a limb, you're taking a risk because the limb could break and you could fall to the ground and hurt yourself.

"a law unto themselves"

If somebody is a law unto themselves, they do things their own way and follow their own ideas about how to live instead of following what others do.

Our boy Billy is a law unto himself. Of course he sometimes makes mistakes and gets into trouble, but we're proud of him because he doesn't just follow the herd.

Our boss does things a bit differently to most other managers, so it's no surprise that some people say he's a law unto himself.

"throw someone in at the deep end"

If you throw someone in at the deep end, you give them a difficult job to do, or a serious problem to deal with, before they have the knowledge or experience for it.

In her first overseas teaching job, Kathy was thrown in at the deep end with a class of 30 kids and no training, no books, and no guidelines.

Our manager thinks the best way to introduce new staff to the job is to throw them in at the deep end and see how they go.

“Fool around”

“Fool around” is a slang phrase with both innocent and R-rated meanings.

Most of the time, fool around means to play or have fun. A teacher might ask the students to stop fooling around and making so much noise in the back of the classroom. If you fool around with your car, it means you tinker with the engine. You’re not working very hard. You might get fix something and you might not. It doesn’t matter because you’re just fooling around anyway.

Be careful using this phrase though, because fooling around can also mean making out or being physical and romantic with another person.

"go for it"

“Once I started falling in love with swimming, it was easy. I was able to focus and go for it.”

- Olympic swimmer Michael Phelps, on how he became a champion. (Parenting)

When you really go for it, you try your very hardest. You do everything you can to achieve a goal. You don’t hold anything back, even though you might be nervous, scared, or intimidated.

"keep a straight face"

“Dana kept a straight face throughout her brother’s performance, even though she thought he looked very silly as a ballerina.” 

A “straight” face is a serious face. When you have a straight face, you are not laughing, and you aren’t even smiling. You are looking completely normal and calm.

"Drama Queen"

A drama queen makes everything seem more exaggerated and serious than it needs to be.