I am sure you've had this happen to you. Your minding you own business. Your dog comes up and decides to lick you right on the lips. Gross, right? I was listening to the Smart People podcast last night. They had on some dog researcher/expert. They brought up this issue. Though, it's disgusting to humans to be licked on the face, especially the mouth, by a dog, it's actually a show of respect. Younger dogs lick older dogs on the mouth. It's sort of paying respects like we do when we see Grandma and give her a kiss on the cheek. Puppies do it for another reason. It causes the Mom dog to regurgitate. Something we humans really don't want to do! I remember when my brother got his Doberman puppy. Nicki was obsessed with my elderly dog, Sierra. Many times she would walk by Sierra and lick her on the mouth. Sierra never growled or anything. I guess she understood the order of things. Anyway, I thought it was interesting. It doesn't make the mouth kisses any more tolerable. It's nice to think my dog might actually be trying to show me some respect though. (Finally!)