put (one's) back up(redirected from put their backs up)
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put (one's) back up
To be or become angry, hostile, defensive, defiant, or irritable, or to instill such a feeling in someone else. John put his back up when his parents brought up the subject of college. Election season always puts my dad's back up.
get/put somebody’s ˈback upmake somebody annoyed: His silly remarks always get her back up.
This idiom refers to the way cats arch their backs when they are angry.