Green’s Dictionary of Slang

extremely, very, completely, totally; usu. as shitface drunk.

1975		D. Goines Inner City Hoodlum 161: I want this place shit-faced clean within two hours.
1998		Dr Midnite ‘If You Drink Don’t Drive’ 🎵 on Sooner or Later [album] It’s OK to party down / Get shitface drunk and fall on the ground / With some friends around.
2021		J. Ellroy Widespread Panic 8: He was shit-faced drunk at noon.