The word "un-fussy" typically implies an easy-going, relaxed attitude, but there are numerous antonyms for this term that convey the opposite meaning. One antonym might be "meticulous," suggesting a careful and precise approach to tasks or situations. "Fussy," "fidgety," or "nervous" might also serve as antonyms, all conveying a sense of being overly concerned with details or minutiae. Another possibility might be "high-maintenance," which suggests a person or situation that requires a great deal of attention or effort to maintain. Whether positive or negative, using antonyms can help convey a specific meaning or tone when describing different people, places, or situations.