The antonyms for the phrase "mutual fondness" are numerous and depend on the context of the situation. If we talk about feelings or relationships, the antonyms could be dislike, animosity, or enmity. The opposite of mutual fondness could also be indifference, apathy, or aversion. In some cases, the antonym could be betrayal or treachery, particularly when there was a previously mutual fondness that was breached. However, it's important to note that mutual fondness is a dual expression of positive feelings, so many negative emotions could be antonymous. Ultimately, it's the lack of positive feelings, enthusiasm, or loyalty that defines the opposite of mutual fondness.