The result of drinking alot of alcohol, you usally get shit faced when you feel like throwing up, you also get shit faced in the morning when the hang over starts.
So really, shit faced is the period of when you feel like shit after drinking.
Bar Tender - NO ! you have had too much for tonight !
Drinker - Gimme some booze dammit !
Bar Tender - OK ! but only ONE more, you'll end up shit faced and pass out !
Drinker - THANK DRUNK IM GOD !