The term "cleans up one's act" typically means to improve one's behavior or attitude. However, there are several antonyms for this phrase that imply negative behavior. One such antonym is "act out," which means to behave in a disruptive or unruly manner. Other antonyms include "slip up" and "mess up," both of which refer to making errors or mistakes that go against the desired behavior. "Behave badly" is another antonym that suggests someone is not improving their behavior. Finally, "go astray" implies losing focus or straying from the expected path of betterment. These antonyms serve as reminders of what behavior to avoid when trying to clean up one's act.