How do you keep him from licking your face?
I think you need to respect your guests and put the dog on a leash or in a crate when guests come over. If I knew someone was going to allow their dog to give me an unwelcome bath, I wouldn't go there.
You can either teach him NOT to lick people (by using leash corrections and verbal cues, like "no" or "no lick" or "eh-eh") or you can teach him to do something else when guests come over, like go lie on his "place" or go in his crate or lie on his bed. But the longer you allow his tongue free access to your body, the harder it's going to be to break.
I do believe dogs learn what they can do to whom. One of our dogs licks my husband (which he HATES), but she won't lick me because I've taught her not to. They have their own couch, but aren't allowed on any other furniture, etc.
