What is the origin of the idiom "get one's goat" and when to use it?

The origin of the idiom "get one's goat" dates back to horse racing in the early 1900s. It was believed that horses would become agitated and perform poorly if their companion goat, which often kept them calm, was taken away. Thus, if someone wanted to sabotage a competitor's horse, they would "get their goat" by removing the calming influence, leading to a negative impact on the horse's performance. The phrase is commonly used in casual conversations to express discontent or irritation with a particular situation, behavior, or individual.