What is hey is for horses saying?

The saying "hey is for horses" means that someone should stop using a particular word or phrase, as it is considered impolite or vulgar. It is typically used in response to someone using a word or phrase that is considered offensive or inappropriate in polite society. The saying is thought to have originated in the early 20th century and is still commonly used today as a way to gently remind someone to watch their language. It is a light-hearted way of correcting someone's speech without causing offense or confrontation.