1670s, coined by Dryden (as wittycism) from witty on model of criticism.
"That every witticism is an inexact thought: that what is perfectly true is imperfectly witty ...." [Walter Savage Landor, "Imaginary Conversations"]
Formerly often in a good sense, "witty, amusing," but later implying a desire to be amusing that is often intrusive or ill-timed. Related: Facetiously; facetiousness. "Facetiæ in booksellers' catalogues, is, like curious, a euphemism for erotica." [Fowler]
c. 1600, "having an overweening opinion of oneself" (short for self-conceited, 1590s), past-participle adjective from conceit (v.) "conceive, imagine, think" (1550s), a now-obsolete verb from conceit (n.). Earlier it meant "having intelligence, ingenious, witty" (1540s). Related: Conceitedly; conceitedness.