Hello! I have a 13 week old pug who is an absolute delight. Now that he's got his vaccinations, I have started taking him out on a leash.
Being a puppy, he gets really excited when he sees people. I keep him close to me, but if someone asks if they can pet him, I let them do it, warning them beforehand that he gets rather excited and will try to climb up their legs and lick them 
So far so good, except that a couple of times I have noticed him getting way too excited, a bit frantic in fact, so I've taken him in my arms and when I have done so, he's bitten me in the arm. Not nipping, but actual hard biting. He's also done this at home after some playing.
We are starting puppy training classes this week so of course I will ask the trainer, but since it's 6am and I'm insomniac I thought I'd ask here too.