A "slip" makes drinking sound accidental, as if the drinker was an innocent bystander in the process. There is nothing accidental about putting a bottle to your own lips. Bottom line is that anyone who "slips" made a conscious decision to drink. Period. It's not unforgivable by any means, we are all human and we all have struggles. However, I do think it's best for the alcoholic if they own up to their mistakes, rather than trying to hide behind frilly terminology.