Don't bother to speak; save your breath (as your request will not be granted or is futile).
我知道你想借用我的车，但这次你还是免开尊口吧，我周末也要用。
I know you want to borrow my car, but this time you'd better save your breath; I need it myself this weekend.
Next Idiom
Don't bother to speak; save your breath (as your request will not be granted or is futile).