Green’s Dictionary of Slang

1. a worthless, insignificant or objectionable person; frequently used as a term of contempt, e.g. you slag!

c.1786		Grose Classical Dict. of the Vulgar Tongue ms. additions n.p.: Slag. A Slack metald fellow.
1788, 1796		Grose Classical Dict. of the Vulgar Tongue (2nd, 3rd edn) n.p.: Slag. A slack-mettled fellow, one not ready to resent an affront.
1811		Lex. Balatronicum.
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue.
1943		W. Buchanan-Taylor Shake It Again 199: A slag is a person who is not much bottle – not much good; [...] for whom you have no respect or time [OED].
1956		‘Charles Raven’ Und. Nights 166: You slag! What did you want to take these for?
1958		M. Pugh Wilderness of Monkeys 89: Sit down [...] you slag.
1959		F. Norman Fings I i: No-one wants to know him except the few slags that go up his shpieler.
1961		J. Sparks Burglar to the Nobility 120: Underworld people — I mean burglars and real performers, not slags and petty cheats.
1962		Parker & Allerton Courage of his Convictions 159: When I got out there was some slag on the door, all gold braid and nose in the air.
1971		T. Lewis Plender [ebook] He was a tight-fisted old slag.
1978		L. Kramer Faggots 36: It’s easier to do it myself than to trust just any slag.
1978		R.D. Pharr Giveadamn Brown (1997) 77: The slag, the driftwood, the grifters and the scum would all come by.
1979		F. Norman Too Many Crooks Spoil the Caper 215: Grasses ain’t nuffink but right slags in my book.
1981		A. Payne ‘You Need Hands’ in Minder [TV script] 10: He must have flogged the motor, the rotten slag.
1989		in G. Tremlett Little Legs 111: Their clubs brought together villains, slags and show business people.
1993		M. Dibdin Dying of the Light 97: Letty may be a foul-mouthed slag who might be compared to a brick outhouse to that edifice’s advantage.
1998		M. Newall ‘Sir Gawayne and the Grene Knight’ in Indep. Weekend Rev. 26 Dec. 1: Come over here iffe yow thynk you’re harde enough. You slagge.
1999		Indep. Rev. 10 July 4: Right, you slag, you’re nicked!
2000		Guardian G2 11 Apr. 6: I’ll let them dirty slags do what they want with her.
2006		in D. Seabrook Jack of Jumps (2007) 80: A little slag, a flash boy.
2010		L. Redhead Thrill City [ebook] It was all coming from Beverly, the puritanical slag.

2. a rough or brutal person.

1934		P. Allingham Cheapjack 237: The Newcastle ‘slag’ is the sort of man who makes up the personnel of the race-gangs, and [...] he will pick a fight with anyone.
1955		B. Hill Boss of Britain’s Underworld 95: He was what we call a bit of slag, just a small-time tearaway who tried to make himself big by the use of a razor or shooter.
1961		New Statesman 14 Apr. 576/2: As the underworld put it, ‘he steamed in like a slag and roughed them up as he topped them.’.

3. rubbish, nonsense.

1948		V. Palmer Golconda 35: ‘Listen,’ he said [...] ‘There’s some men in every camp will get a kick out of throwing dirt. Who’s been filling you up with slag about me? That old crank up on the mountain, was it?’.
1966		T. Keyes All Night Stand 79: We don’t play Zippadee-do-da anyway, but Mojo or something that is real old slag now.
1977		C. Hope Ducktails in Gray Theatre Two (1981) 40: Listen Howellsie. Don’t chat us sleg now.

4. orig. of criminal loot, cheap or worthless items.

1955		B. Hill Boss of Britain’s Underworld 30: With my mob we might do as many as twelve screwing jobs before we got a real tickle. The first eleven jobs might bring us a bit of slag: wireless sets, sheets, a bit of chap tomfollery.
2002		Guardian 17 July 19/1: Pot Noodle’s self-description as ‘the slag of snacks,’ a downmarket, trashy product.

5. a vagrant, a petty criminal; thus the slag, such persons collectively.

1955		P. Wildeblood Against the Law 120: Several different kinds of burglars [...] the rank amateurs or ‘slags’ who had stolen paltry sums.
1962		R. Cook Crust on its Uppers 22: The terrible thing about the slag, though, is that they actually survive.
1970		P. Laurie Scotland Yard 141: I could get them up the nick and take their prints with ink, but that’s really for slag.
1999		Indep. on Sun. Culture 11 July 1: Some slag having his fingernails peeled off one by one in a back room.

6. a prostitute, a promiscuous woman, a slattern; thus such persons collectively.

1958		F. Norman Bang To Rights 72: She must be a right slag, my old woman wouldn’t do anything like that.
1963		N. Dunn Up the Junction 6: If you was an old slag, I’d just say, ‘Come ’ere ...’.
1977		A. Bleasdale Who’s Been Sleeping in my Bed 27: She doesn’t flash it about [...] not like some of the white slag on the estate.
1985		R.G. Barrett You Wouldn’t Be Dead for Quids (1989) 165: You’ll probably pull some slag [...] and finish up with the jack.
1988		J. Healy Grass Arena (1990) 137: They ain’t no slags; they’re two right little darlings.
1994		G. Disher Crosskill [ebook] ‘Fucking slang,’ Napper said.
1999		J. Cameron Brown Bread in Wengen [ebook] ‘[Y]ou do a bit of the old massage or you some MP’s slag or what?’.
2005		B. Hare Urban Grimshaw 3: There’s an ugly fucking buah, called Trudi, the slag, / and we all hate her because she’s a bag.
2011		Eve. Standard 9 May 15/4: Along with other patriarchal taunts—slang, slapper, ho—that are so common in the teenage lexicon.
2011		J.J. Connolly Viva La Madness 98: I’ll do ya up the shitter [...] You love it up the dirtbox, you posh slags!
2015		I. Welsh Decent Ride 121: A real slag will ey ride aboot thaire’s nowt ye kin dae aboot it.

7. (N.Z. prison) a prioner who does jobs for more influential inmates.

2001

D. Looser Boobslang [U. Canterbury D.Phil. thesis] 169/1: slag n. = bum boy sense 1; tea boy sense 1.