(one's) line of country British phrase
A subject one is knowledgeable or likes a lot
Maths is my line of country. I could spend hours unraveling the mathematical puzzle.
Psychology is her line of country. She has treated a number of emotionally disturbed children.
Realizing that cooking is my line of country, I decided to pursue vocational education to be a skilled chef rather than attending university.
I have quitted my current job because it is not my line of country.
Have a strong feeling of affection for someone or something
To have experience and understand of how bad or unplesant something is
If you are in/get into somebody's good/bad books, you have/not have their favour.
To give someone or something better treatment than others.
Know a lot about something
The origin of this phrase is not clear.
If you swallow the bait, you take something that someone offers you, or agree to do something that someone asks you to do without knowing that it is a trick or way of getting something from you.
You can't just do whatever he wants you to do. Don't swallow the bait.