"treat with disdain or contempt" (transitive), 1550s, intransitive sense "mock, jeer, scoff" is from 1570s; of uncertain origin; perhaps a special use of Middle English flowten "to play the flute" (compare Middle Dutch fluyten "to play the flute," also "to jeer"). Related: Flouted; flouting.[flout etymology, flout origin, 英语词源]