The antonyms for the phrase "behaving badly" could vary according to the context of the situation. In general, the term could be replaced with phrases like "acting appropriately," "displaying good manners," "exhibiting proper conduct," "following etiquettes," "showing respect," "behaving well," "behaving maturely," or "being well-behaved." An alternate approach to the phrase could be to focus on positive traits or actions, such as "being polite," "displaying kindness," "showing consideration for others," "being compassionate," or "demonstrating empathy." Whatever the replacement term may be, it should convey a more positive and constructive behavior or characteristic.