A tatterdemalion is a tattered or ragged person.
It’s a lively, rattling, machine-gun word, one chosen by many writers as suitable accompaniment to invective or disparagement. Here’s Lady Wishfort, in William Congreve’s play The Way of the World: “Frippery? Superannuated frippery? I’ll frippery the villain; I’ll reduce him to frippery and rags, a tatterdemalion!”. Or James Joyce, in full flow in Ulysses: “Florry Talbot, a blond feeble goosefat whore in a tatterdemalion gown of mildewed strawberry, lolls spreadeagle in the sofa corner, her limp forearm pendent over the bolster, listening”.
But where it comes from is open to argument. The first part seems pretty certain to be our English tatter. Some writers trace the second bit to the French maillon, swaddling clothes. Others say it comes from the Italian maglia for undershirt or (British English) vest. Support for this comes from the very earliest use, by Ben Jonson in 1611, which he spelt as tatter-de-mallian, reportedly said as though it were Italian.