Learning a language takes time and effort due to its complexity. Language is forever changing. What is currently popular may be replaced by something else in years to come, and the use of slang is a strong testament to that. Colloquial expressions are often acceptable in informal writing. The more you learn, the more you will know when to use them or not to use them in your writing or speaking.
Power of: a great deal of.
e.g. Surely he can do anything: he has power of money.
Hold your horse: delay taking action.
e.g. Come on, hold your horse, and just take it easy!
Right you are: I agree.
e.g. "I think I'm going to accept this job." "Right you are."
All at sea: confused.
e.g. "What do you think of the proposal?" "I'm all at sea; I'm completely clueless."
Give someone a piece of one's mind: scold.
e.g. He was rude, and I would like to give him a piece of my mind.
Pop the question: propose marriage.
e.g. Did he pop the question on Valentine's Day?
All hot and bothered: agitated, confused, or excited.
e.g. She was all hot and bothered when she heard the news of their divorce.
Poorly: sick or unwell.
e.g. What's the matter with you today? I say, you look poorly!
Easy on the eye: good looking.
e.g. I say, your girlfriend is easy on the eye.
e.g. I was pooped after working for nine hours in the yard.
Say one's piece: say what one ought to say.
e.g. I must say my piece: that was not a nice thing to say to your parents.
Give someone a break: leave me alone.
e.g. Come on, give me a break; I don't want to hear this from you.
Copyright© by Stephen Lau