Ορισμός και Σημασία του "my foot"

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

The idiom "my foot" is an informal expression that is used to express strong disagreement, disbelief, or rejection of a statement or claim. It is a shortened form of the phrase "not on your foot" or "not on your life," which originated in the early 20th century.