Learning a language takes time and effort, especially if it is not your first language. Even if it is your mother tongue, you still need time and effort to master it. 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.
Hell-bent on: very determined.
e.g. The team is hell-bent on winning the game tonight.
Not born yesterday: not as naive or foolish as you think.
e.g. Don't give me all that nonsense. I was not born yesterday.
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."
Get cold feet: become anxious and fearful.
e.g. He got cold feet, and left without taking the challenge.
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!
Saw you coming: realized your ignorance.
e.g. You gave him the money right away without asking any question; he saw you coming!
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.
Copyright© by Stephen Lau