Định Nghĩa và Ý Nghĩa của "my ass"

What is the origin of the idiom "my ass" and when to use it?

The origin of the idiom "my ass" is unclear, but it has been around for a while. It is a casual and straightforward way that people use to say they do not believe something or disagree with it. This expression is often used in informal conversations and can be offensive at times.