Green’s Dictionary of Slang

(Aus.) a general insult, usu. aimed at an old man, esp. an alcoholic.

1900–10		Stephens & O’Brien Materials for a Dict. of Aus. Sl. [unpub. ms.] 43: CHAT: Austral. thieves man.
1967		‘Whisper All Aussie Dict.’ in Kings Cross Whisper (Sydney) xxxiii 4/3: chat: [...] A term used to describe an obnoxious person.
1973		J. McNeil Chocolate Frog 104: Bulla: ‘All I do know about you, is that yer an old chat: a drunken old deadbeat bum that tells war stories’.
1974		Adamson & Hanford Zimmer’s Essay 46: A chat who smelt of white lady swilled and puked. [Ibid.] 99: In New South Wales prison argot, it means both ‘louse’ and a certain type of prisoner. A ‘chat’ is a social incompetent, though not necessarily drunk.
1983		R. Aven-Bray Ridgey-Didge Oz Jack Lang 22: Chat Derelict person.
1984		B. Ellem Doing Time 187: chat: a person [in prison] who is a sloppy, dirty dresser.
1990		Tupper & Wortley Aus. Prison Sl. Gloss. 🌐 Chat. A person who is a [sic] sloppy or dirty in their habits or dress. Often applied to vagrants serving short sentences.
1996		(con. 1964-65) B. Thorpe Sex and Thugs and Rock ’n’ Roll 284: Anyone who didn’t bother to take care of their shoes or who had grotty clothes was regarded as a ‘chat’, and to be called a chat was a low insult.
2001		D. Looser Boobslang [U. Canterbury D.Phil. thesis] 40/2: chat n. a dirty person, a person who does not wash regularly, specifically applied to tramps.