a question for anyone with dog behavior knowledge

Can you tell me why my Great Dane puppy (8months) play fights with my son (19) when my son has him jump to his chest (like "give me a hug") paws at shoulders. he mouths at him (not biting) and low growl. My son doesn't like or encourage him to do this and he doesn't do it with anyone else who let's him jump on them like that. It becomes a conflict because it irritates my son and I don't like it. Does anyone know what the dog is "saying" when this happens. Just the other day my brother - n- law let him do that and he just licked his face and did mouth him but no growling or getting too out of control. I've told my son not to let him do it all, but he likes getting the hug and other people let the dog do it too. Sorry if this is confusing, and please only respond if you know what I'm trying to say and you have a suggestion.

I'd have to see the interaction between the puppy and your son at other times - but, this puppy at 8 months is now like a teenage male (hormonally). If the puppy jumps up on other people's shoulders with no growling involved, there's something in his relationship with your son (or how the dog perceives it) that's causing it.

For now at least, your son has to stop letting him jump up on him. Sounds like the puppy is beginning to think he's the alpha in that relationship. Suggest to your son that he do a little simple obedience with the puppy (at home only, no classes). Work on sit, stay, down, come and heel. Give the dog lots of praise, treats or both. Simply obeying your son's commands should change this relationship back to where it should be.