The term "haddest tantrum" implies a situation where someone has thrown a fit or became angry and emotionally overwhelmed. Antonyms for "haddest tantrum" could include words such as calmness, serenity, peace, composure, and poise. The opposite of a tantrum is a display of self-control, patience, and maturity. Antonyms like tranquility, placidity, calmness, and peaceableness indicate an absence of anger or emotional turmoil. Such antonyms suggest traits of someone who is level-headed, restrained, and composed. Therefore, by using antonyms, we can depict an entirely different atmosphere from the chaos and fuss that comes along with a person who had a tantrum.