The phrase "took one on" is often used informally to describe someone taking on a challenge or facing a difficult situation. However, there are many antonyms to this phrase that can be used to convey a different message. Some potential antonyms for "took one on" include giving up, avoiding, shirking, evading, and surrendering. Depending on the context of the situation, these antonyms may be used to describe a different outcome or response. It's important to consider the nuance of language and the meaning of different words when trying to convey a specific message, as the choice of words can greatly impact the tone and perception of the conversation.