Idioms in English

Devil's Advocate - a person who expresses a contentious opinion in order to provoke debate or test the strength of the opposing arguments.
Example: Teachers often play devil's advocate to provoke discussion in the classroom.

Curiosity killed the cat - being inquisitive about other people's affairs may get you into trouble.
Example: Don't ask about his break-up, curiosity killed the cat!

What you sow is what you reap - You eventually have to face up to the consequences of your actions.
Example: If you treat your friends like that, of course they drop you. You reap what you sow in this life.

A dime a dozen - very common and of no particular value.
Example: Water is treated as a dime a dozen. That is why people waste it.

Beat around the bush - To avoid getting to the point of an issue
Example: She never told her friend the truth. She kept beating around the bush.

Cold shoulder - a phrase used to express dismissal or the act of disregarding someone.
Example: He offered a cold shoulder when a stranger asked for help.

Fit as a fiddle - in very good health.