Green’s Dictionary of Slang

having consumed a large volume of alcohol in a very short time.

1999		Guardian G2 11 Nov. 6: A few years of being rat-arsed, smashed, loaded, leathered, pissed.
2000		Guardian 14 Jan. 32: Little bird tells me DT was out last night getting leathered toasting Gary Neville.
2012		R. Milward Kimberly’s Capital Punishment (2023) 225: I was looking forward to getting leathered.
2023		S. Moore Letters from Suzanne 3 Dec. 🌐 ‘What sort of person gets leathered in a Wetherspoons in Gatwick at 10am?’ I saw someone tweet this recently.