1. A stupid or eccentric person.
2. A typographical device other than a letter or numeral (such as an asterisk), used to signal divisions in text or to replace letters in a euphemistically presented vulgar word.
- Oxford Dictionaries
Dingbat is a bit of American slang that first appeared in 1838, where it was used to refer to an alcoholic drink. We aren't sure what drink this may have been, and it is likely that it was already being used in the same sense that would later become common -- a silly or foolish person -- but its history is rather muddled. As Online Etymology Dictionary says:
"Used at various periods for 'money,'1 'a professional tramp,' 'a muffin,'2 'a typographical ornament,'3 'male genitalia,' 'a Chinese,' 'an Italian,' 'a woman who is neither your sister nor your mother,' and 'a foolish person in authority.'"
Yeah, well, they gave up too easy. It has also been used to mean a bullet, a cannonball, a dingleberry, a batman4, a slap to the buttocks, an argument, an affectionate mother's hug, a generalized term of admiration, and perhaps most unsurprising of all, as a term for anything that one cannot recall the proper name for.
Oh, and also, it was used as an adjective referring to a foolish person (allowing, at least technically, for the construction "he's a dingbat dingbat").
So... back to the modern usage. In 1909 the "foolish person" usage was given a big boost by George Herriman's popular cartoon The Dingbat Family, (later changed to The Family Upstairs). This was probably sufficient to make it stick, but many of the alternate meanings (batman, italian, chinese, tramp) came into use after this. The current comparative uniformity of usage is due to its appearance in the popular 1971 TV show All in the Family.
Feeling that all this was not enough, the New Zealanders coined dingbatisis in the 1920s, meaning alcoholism.
Footnotes:
1. A generic term, such as moolah.
2. Also a generic term.
3. More familiar to many of us as a typeface akin to windings; the original dingbat typeface was composed of stars, bullet points, and checks and exes, but it is common to find variants with street signs, Christmas art, and anything else that humans might want to put on paper.
4. In the sense of an officer's servant.