Basically the same thing as a Designated Driver. They go with a group of friends to a party but don't actually participate in drinking but they drive their drunk friends home.
A dog trained to guide his master when the master becomes extremely intoxicated on alcohol or other drugs. The dog aids the master in continuing to function as if he were still a sober human being. Similar to a seeing eye dog but the people for whom the sober eye dog assists are fucked up drug heads and not actually blind.
Jim: I am afraid John is too fucked up to make his walk home.