Off one's rocker is a colloquial idiom that means someone is behaving irrationally or acting in a chaotic manner. Some antonyms of this expression might be logical, sensible, and rational. When we use the phrase off one's rocker, we usually refer to someone who is a bit crazy or mentally unbalanced. By contrast, antonyms like sound, steady, and reasonable describe people who are mentally stable, able to control their emotions, and make sound decisions. Using these antonyms can help us understand the contrast between someone who is behaving erratically and someone who is living life on an even keel.
