"Be sweet on" is a phrase that can be used to describe an infatuation or attraction someone feels towards another person. Some antonyms for this phrase may include "dislike," "abhor," "detest," "despise," or "loathe." These words signify a complete opposite to the positive and affectionate connotations of "be sweet on." The person in question may actively go out of their way to show that they are not attracted to the other person. It's important to note that these antonyms may not always be used in the context of romantic relationships and can be applied to any situation where one may hold negative feelings towards another.