Green’s Dictionary of Slang

goofball n.2

[goof n.1 (3) + -ball sfx]

(US) a silly, amusing, eccentric or insane person.

[US]J.M. Inks diary Eight Bailed Out (1954) 29 July 48: ‘Dig this goofball,’ Griff said.
[US]B. Schulberg Waterfront (1966) 258: There’s no room for goof-balls in this business.
[US]W.C. Anderson Adam M-1 83: I seem to have a penchant for attracting the greatest collection of goof-balls.
[US]L. Bangs in Psychotic Reactions (1988) 130: The band themselves come on like total goofballs.
[US]W.M. Henderson Stark Raving Elvis 8: Byron [...] glared back at the goofball.
[US]P. Cornwell From Potter’s Field (1996) 186: Her dad died. You’re divorced. She’s got no brothers and her mother is in and out of bed with goofballs.
[US]Mad mag. Feb. 35: After allowing the liberal goofball two sentences O’Reilly spins lengthy, elaborate scenarios [etc.].