Giving the nod is a gesture of approval or agreement, but there are plenty of antonyms for this phrase that imply disapproval or disagreement. An antonym for giving the nod is shaking the head, which shows disagreement or refusal. Ignoring someone is also an antonym, as it means to not acknowledge their request or idea. Rejecting or vetoing an idea or proposal is another antonym for giving the nod, as it implies a negative response. Lastly, criticizing or condemning someone or something is an antonym, as it implies disapproval or disfavor. These antonyms show that there are many ways to express disagreement, and giving the nod is just one of them.