Antonyms of fussy :
plain, unfastidious, good-natured, affable, agreeable, amiable, genial, good-humored, good-tempered, gracious, well-disposed, accommodating, complaisant, obliging, easygoing, laid-back, relaxed, forbearing, long-suffering, patient, stoic, tolerant, uncomplaining, breezy, carefree, devil-may-care, happy-go-lucky, lackadaisical, low-pressure, flexible, lax, loose, lenient, permissive, uncritical, indiscriminating, undiscriminating, undemanding, unfussy, cursory, halfhearted, heedless, inattentive, incautious, mindless, regardless, unguarded, unsafe, unwary, neglectful, negligent, slipshod, sloppy, slovenly, imprecise, inaccurate, bold, impetuous, rash, reckless, apathetic, indifferent, lazy, lazyish, careless, bare, denuded, exposed, naked, stripped, uncovered, modest, simple, unassuming, unpretentious, conservative, muted, quiet, restrained, subdued, tasteful, toned-down, understated, unobtrusive, austere, severe, stark, unadorned.
Examples of usage:
These boys were slovenly players, and were made unhappy by Skepsey's fussy instructions to them in smartness. "One of Our Conquerors, Complete", George Meredith Last Updated: March 7, 2009.
When Miss Maggie remonstrated at the size of the increase, he pooh- poohed her objections, and declared that even that did not pay for having such a nuisance of a boarder around, with all his fussy notions. "Oh, Money! Money!", Eleanor Hodgman Porter.
Now don't make any more noise, for William is fussy. "The Curlytops on Star Island", Howard R. Garis.