Accidental
inebriation. If "to shart" is the act of intending to fart but
accidentally shitting yourself, and "shit-faced" is the state of being
intoxicated, then it follows that "shart-faced" would be a condition of drunkenness reached only by accidental or unintentional means.
Honey, we only went out for
a couple of beers but Mel kept ordering these little shots of
blue shit and the next thing
you know we're all completely shart-faced.