When it comes to antonyms for the phrase "exchange greetings," the possibilities are vast. One could ignore someone or snub them, indicating a lack of interest or respect. Alternatively, one could simply remain silent, failing to acknowledge the other person's presence or existence. In some cultures, it's customary to offer a physical gesture in greeting, such as a bow or handshake, so refusing to do so could also be considered an antonym. The key point is that any action that indicates a lack of interest, respect, or willingness to engage with the other person can be considered an antonym for exchanging greetings.