Took one up on is a phrase that refers to accepting or agreeing to a challenge, invitation or offer. Its antonyms are words that imply rejection, refusal or avoidance of a challenge, invitation or offer. Some antonyms for took one up on are declined, rejected, ignored, neglected, dismissed, avoided, evaded, and turned down. These words indicate a lack of interest, motivation or willingness to participate in the proposed activity. While taking someone up on an offer shows enthusiasm and a proactive attitude, declining it could suggest disinterest, shyness or reluctance. Therefore, choosing the appropriate word to describe the response to a proposal is essential to convey the right message.