The Collaborative International Dictionary
ding-a-ling \ding"-a-ling\ a stupid or foolish person; -- used in a deprecatory or contemptuous sense. [slang]
Syn: dingdong, doofus. [PJC]
Douglas Harper's Etymology Dictionary
"one who is crazy," 1935, from notion of hearing bells in the head (see ding (v.)).
Wiktionary
n. 1 The sound of a small bell; the sound of a fire engine bell. 2 (context US English) An eccentric or crazy person. 3 (context slang English) The penis.
Wikipedia
"Ding-A-Ling" is a song released by Bobby Rydell in 1960. The song spent 11 weeks on the Billboard Hot 100 chart, peaking at No. 18. Paired with its flip-side, Swingin' School, "Ding-A-Ling" reached No. 1 in Australia and No. 2 on Canada's CHUM Hit Parade.
Usage examples of "ding-a-ling".
THE CORNER of the parking lot Dirk Pardee watched the confrontation between Fairbank and the ding-a-ling major.