My dog bared his teeth and growled at my daughter's friend (she's 14) today. She had tried to give him a "hug", which might explain it a bit, but he is very used to children and people fussing him and so far his temperament has been fine. We had to change training classes recently, because our old one closed, and he has been a bit "down" at the new one, which we have now stopped as there were so many aggressive dogs, and they didn't seem to be under control so he was getting stressed out. I'm having him checked out at the vet tomorrow to check that there isnt' something medically wrong, but wanted to see if anyone else has had a dog suddenly turn like this, against character? He is nearly 2 now.
Thank you.

What breed?

Many years ago my daughter who was 5 at the time was bitten on the face by one of my dogs. I did not see what had happened and asked her what she did (never thinking it would be the dogs fault). She said she went to hug him. So, I asked her to show me what she did.  Kneeling down she was smaller than the dog and her arm went across the front of his chest and the other round the back of his neck.  I checked the area and discovered an abscess, not a large one but very painful all the same. It was in just the right place for my daughters elbow to make contact, no fault on dog or child but a very painful abcess gone un-noticed. If this is completely out of character for the dog, please check for any medical problems visible or otherwise.

I wrote not long ago about one of my dogs being a bit off with folk and after a trip to the vets we discovered she too has asmall absess on top of her head.We could not see it as she has a double coat but when  her fur fell out it really did look painfull even though it was small.Now it is healing she is back to her old self,thankfully.

Also a 14 year old stranger would not be perceived as a child and trying to hug a dog just reaching maturity would be perceived as either threatening or dominating and rude, so he told her to get out of his face in teen speak. 

This can be a difficult time for maturing dogs when they are trying to establish their role in the gradn scheme of thigns.  As he is now adult you may have relaxed a bit with his training and he has just got a bit above himself, which he might not dare demonstarte with family, but thought it fair to your daughters freind.

To be honest a dog should not be hugged by non family members unless the dog is seeking the attention.

Imagine visiting one of your freidns who your daughter didn't know well, and they gave her a big hug, as a tenager whe would most likely not be impressed, and adult would take it in their stride.