Get one’s back up is an idiom that has been in use for some time. We will examine the meaning of the common saying get one’s back up, where it came from, and some examples of its idiomatic usage in sentences.
To get one’s back up means to become obstinate or hostile, to become annoyed, and to get ready to fight or argue. The idiom get one’s back up describes getting angry or defensive. Often, the term is used in the negative as an admonition, as in don’t get your back up. The phrase get one’s back up came into use in the 1700s; the image is that of a cat arching its back in an aggressive posture. Related phrases are gets one’s back up, got one’s back up, gotten one’s back up, getting one’s back up.
Resist the urge to get your back up with a “get off my lawn, punk” snarl. (Modesto Bee)
Before you get your back up listen to what they say, not how they’re saying it. (Sydney Morning Herald)
And don’t get your back up when you don’t like something you hear. (La Grande Observer)