The word "most fun loving" suggests someone who is full of life and loves to have a good time. Antonyms for this phrase could include words like serious, gloomy, and reserved. These words describe individuals who tend to be more introverted and are not as interested in socializing or engaging in lighthearted activities. They may prefer more intellectual pursuits or spend their free time alone. Alternatively, synonyms for "most fun-loving" may include words like playful, enthusiastic, and outgoing, which suggest someone who is full of energy and likes to be around others. Ultimately, the opposite of "most fun loving" is someone who is more subdued and less inclined to seek out excitement.