When people say that something "really gets my goat,” they mean that they are extremely irritated. A wide variety of things could contribute to irritation, ranging from someone else's actions to a series of events, but, despite the turn of phrase, goats are not usually involved. Like many colorful idioms in the English language, the origins of “get my goat” are murky, difficult to pin down, and actually rather fascinating.
Basic Meaning
If a person says, "that really gets my goat," he or she is simply expressing that an occurrence or object has caused annoyance. The "that" in the statement might not even refer to an actual thing, but rather to a situation. It is also common for a person to direct the phrase at someone else as "you really get my goat," to indicate that the object of the comment is annoying the speaker.
Early Usage and Possible Origins
The first recorded uses of the phrase crop up around the early 1900s, and seem to suggest that this idiom is American in origin. This time period was, in fact, a great era for colorful slang terms in America, reflecting the rapid expansion of settlement in the US and the commingling of people from a wide variety of social, class, and ethnic backgrounds. A number of slang terms from this era are undoubtedly corruptions of slang from other languages, or misunderstandings of English words. Some people have suggested that “gets my goat” may be related to “goad,” as in “to irritate.”
Possible Roots in French
This fairly mundane explanation has been eclipsed by a number of other interpretations of the slang term. Some people have suggested that the term is a translation from the French prendre la chèvre, “to take the goat,” an idiom from Old French which references taking someone's form of income. For low-income French peasants, the theft or a goat would be a catastrophe, as the animals provided milk and meat for their owners. However, this may be a backformation, which is a connection made after the fact, rather than an explanation of "gets my goat."
Connections to Horse Racing
One of the most interesting explanations behind “gets my goat" involves racing horses. As early as the 1700s, goats were used as companion animals to help settle race horses, keeping the notoriously skittish animals relaxed. Taking a horse's pet goat away would have agitated and upset the animal, potentially influencing the outcome of a race.
The practice of providing race horses with companion animals is still widespread, with horses bonding with ponies, chickens, dogs, and a variety of other animals in addition to goats. Many horses do indeed become deeply attached to their companions, exhibiting considerable stress when these animals are removed. Someone taking away a companion animal could negatively impact a horse's performance, and such incidents may have inspired the idiom “gets my goat” among observers.