The antonyms for the phrase "act up on" include words like ignore, disobey, neglect, reject, and disregard. When we act up on something, we are typically following through on some sort of directive or taking action based on a particular idea or concept. By contrast, when we ignore something, we are actively choosing to overlook it or place it on the backburner. Disobey and neglect suggest a more intentional disregard for a task or responsibility, while rejecting something means that we are actively opposing or dismissing it outright. Regardless of the antonym used, each word represents a different way in which we might choose to respond (or not respond) to a given situation.