The phrase "giving nod" is often associated with agreement or approval. However, there are several antonyms that can be used to convey a different meaning. For example, "shaking head" can indicate disagreement, disapproval, or rejection. "Ignoring" or "disregarding" would suggest a lack of interest or attention. "Frowning" can indicate displeasure or dissatisfaction. "Rejecting" or "denying" would indicate a complete refusal or repudiation. Overall, there are many effective ways to express the opposite of "giving nod," depending on the specific context and the intended message.