Language is forever changing. What is currently acceptable or popular may be replaced by something else in years to come, and the use of slang is a strong testament to that. Slang is just an alternative way of saying something. It is sometimes hard to identify what is slang and what is not. Slang and colloquial expressions are often acceptable in informal writing because they are used in communication in movies, newspapers, radio, television, and the media.
Easy on the eye: good looking.
e.g. I say, your girlfriend is easy on the eye.
Beefcake: a muscular man.
e.g. She has been dating a beefcake.
e.g. He goes to the gym regularly because he wants to be a beefcake.
Caught short: caught at a disadvantage.
e.g. The market plunged, and we were caught short just as thought we were on the road to recovery..
Killer: a very funny joke.
e.g. That last one was really a killer; everybody laughed.
Kick back: relax and enjoy.
e.g I really want to kick back and enjoy the music.
Daylight robbery: too costly.
e.g. That’s daylight robbery; to pay $300 just to fix this!
Not in the same street: of a different quality (usually inferior).
e.g. These two dresses may look similar, but they are not in the same street. This one looks much more elegant than that one.
Alive and kicking: in good health.
e.g. "How is your grandmother doing?" "Very much alive and kicking."
Bad shot: wrong guess.
e.g. “He came with his wife, didn’t he?” “Bad shot: he came all by himself.”
In a jiffy: soon.
e.g. The manager will see you in a jiffy.
Next to nothing: hardly anything.
e.g. “Did she leave you anything at all?” “Well, next to nothing.”
Not so dusty: quite good.
e.g. Well the performance was not so dusty; much better than I expected.
Whistle for: wish in vain.
e.g. The stock market has fallen sharply. You can whistle for your money invested.
Head above water: out of debt.
e.g. Nowadays, it is not easy to keep your head above water.
e.g. Can I borrow a little mean-green from you?
Break a leg: good luck!
e.g. "I'll have my first piano competition tomorrow." "Break a leg!"