Slouchiest refers to someone who is lazy or sits in a hunched or drooping position. Antonyms for this word include upright, alert, energetic, efficient, and active. People who are upright are confident and self-assured, displaying good posture and a positive attitude. Alert individuals are attentive, vigilant, and quick to react, while energetic people are full of life and enthusiasm. Efficient individuals are organized, productive, and able to complete tasks with minimal waste of time and energy, and active people are always on the move, engaged in physical activity or other forms of work. Opposite of slouchiest are people who are productive, energetic, and highly motivated.