it goes without saying; unnecessary to explain because it is obvious

Used to describe someone who is completely unscrupulous and will use any means necessary, however base or despicable, to achieve their ends; often refers to committing all manner of crimes or evil deeds.

To prepare something for future or emergency use while keeping it idle for the time being; to keep something in reserve

don't mention it; a polite response when someone thanks you, meaning there is no need to stand on ceremony

not paying attention; careless or lacking in focus; not putting one's heart into a task

let alone; to say nothing of; not to mention

Polite response to someone saying thank you, meaning "you're welcome" or "don't mention it".

Idiomatic phrase used to tell a server or driver that they do not need to return the change after a payment