Nouns

(n)zanya buffoon in one of the old comedies; imitates others for ludicrous effect
(n)fathead, goof, goofball, bozo, jackass, goose, cuckoo, twat, zanya man who is a stupid incompetent fool

Adjectives

(s)goofy, silly, wacky, whacky, zanyludicrous, foolish“wore a goofy hat”, “a silly idea”, “some wacky plan for selling more books”
(s)buffoonish, clownish, clownlike, zanylike a clown“a buffoonish walk”, “a clownish face”, “a zany sense of humor”