Mud in your eye is a proverbial expression that is often used upon ceremonially clinking glasses, or after toasts.
It is a synonym to cheers or bottoms up, meaning that one should drink from his alcoholic beverage, as the toast is concluded.
The use of the phrase can be traced back to the 19th century, but its exact story of origin is currently unclear.
It is used more frequently in British English, and not so much in American English, so it is believed that the term originates from the British Islands.
There are two theories about the origin of this phrase.
The first one is about British soldiers fighting in World War 1, who lived in trenches and were covered in mud all the time, which led to the use of this term.
The second one believes that it is a reference to the Bible, in which Jesus heals a blind man by smearing mud over his eyes.
People have been using this phase since the 19th century in various situations, but the most common way is after a toast.
Over the years, it also became a term that is used in horse racing.
The winning horse kicking mud into the eyes of the horses that ride behind it is a common phenomenon on racetracks.