The expression "shake hands on it" is often used to seal a deal or agreement between two parties. Antonyms for this phrase would include phrases such as "disagree," "refuse," or "decline." These words imply that an agreement has not been reached or that one party is unwilling to go along with the other's terms. Other antonyms might include "renounce," "oppose," or "dispute," which suggest a complete lack of willingness to establish any form of agreement. Overall, it is important to recognize that reaching an agreement often involves active communication, negotiation, and compromise, rather than simply shaking hands.