The antonyms for "hit up on" could be "avoid," "ignore," or "neglect." These words indicate a lack of interest or intention to approach someone or something, instead choosing to keep one's distance or focus on other matters. "Disrespect" or "demean" could also be considered antonyms if the context involves unwanted or unwelcome advances towards another person. While "hit up on" typically implies a positive or flirtatious interaction, its antonyms paint a picture of disinterest or even negativity towards the subject at hand. It's important to consider the connotation of these words in light of the specific situation they are being used in.