GOOFBALL

clown, buffoon, goof, goofball, merry andrew

(noun) a person who amuses others by ridiculous behavior

fathead, goof, goofball, bozo, jackass, goose, cuckoo, twat, zany

(noun) a man who is a stupid incompetent fool

Source: WordNet® 3.1

Etymology

Noun

goofball (plural goofballs)

(informal, often derogatory, sometimes affectionate) A foolish or silly person or animal.

(informal, pharmaceutical drug) A pill or tablet containing a pharmaceutical which has hypnotic or intoxicating effects, especially a barbiturate.

Adjective

goofball (not comparable)

(informal) Silly.

Source: Wiktionary