A bottle of wine and maybe a couple beers keeps me pleasantly drunk for the night. It's not exactly moderate drinking, but I think you'd be surprised how many people can comfortably drink that amount over the course of a night. Not going to pretend it's good for you, but my liver levels and everything else are in great shape in spite of nights like that.

To the original point, if I suddenly started having any kind of pressure or discomfort in the liver region after having even one drink, I'd be in the doctor's office ASAP. It might just be gas or it might be something much worse. It isn't worth waiting around to find out