Simmered down means to calm down or subside. Antonyms for this expression include intensified, heightened, escalated, flared up, and exploded. When things intensify or escalate, they become more heated and emotional. Flared up refers to an outburst or sudden increase in activity, while exploded suggests a complete loss of control. However, when things simmer down, they become less tense or inflamed, allowing for a more peaceful resolution. It is important to remain mindful of these antonyms to maintain control over a situation and avoid causing unnecessary conflict or escalation.