What is the ruling on the saying: "A slap that benefited me"?

There is no objection to using this and similar analogies because their purpose is to help people understand and convey information to them, not to imply the literal meaning contained within them. Moreover, the term "slap" (صفع) is not exclusive to the face; rather, it is used to describe striking the back of the neck or any other part of the body with the palm of the hand.