Where does the term shitfaced come from? I'm aware that it means to be totally drunk, but I'm not sure how shitfaced describes being drunk.
According to Wordorigins.org the theory is as follows...
1960s student slang according to etymology online. Some sites suggest that it’s origin might be from being so drunk that your face is in or near a toilet. I don’t think that can be assumed as fact, however.
Not sure how true it is, as such expressions are seldom tracked.