•Give sb tit for tat (idiom) -

To give someone something equal to what was given you.（以牙还牙，针锋相对）

Examples:

1. They gave me the same kind of difficulty that I gave them. They gave me tit for tat.　　

2. He punched me, so I punched him. Every time he hit me, I hit him. I just gave him tit for tat.

•Give sb a taste of their own medicine（idiom） -

To do the same bad thing to someone that they have done to you. （以其人之道还治其人之身）

Examples:

1. I'm glad somebody decided to give them a taste of their own medicine.　　

2. This team likes to play rough, so let's go out there and give them a taste of their own medicine!

•Spell sth out (phrasal verb) –

To make explicit; to specify in detail.（清楚说明）

Examples:

1. Be assertive and spell out exactly how you feel.　　

2. The government has so far refused to spell out its plans.

•Fall prey to sb/sth (idiom) -

To be harmed or affected in a bad way by someone or something. （深受…之害，成为…的牺牲品）

Examples:

1.　　Police fear that more senior citizens could fall prey to the thieves.　　

2. Some of his friends fell prey to drugs.

•Habit is second nature (proverb) -

That which has been turned into a habitual practice will be done with little or no conscious effort.（习惯是第二天性，习惯成自然）

Examples:

1. Habit is a second nature, so teachers often remind us to make a good habit.

2. Sorry, ever since I worked as an editor I can't help but pick out typos and grammatical mistakes. Habit is second nature!