LOL - I do not envy you having to put up with that. Best advice I can give you is just to ignore it.
Yes, dogs need structure and they need leadership. But leadership is about leading, not finding excuses to interpret every move the dog (in this case, puppy) makes as some sort of Coup d’État for the top spot. Why try to turn everything into that sort of competition? Can't speak for your friend, but there are a lot of people out there who take all the fun out of dog ownership - they misinterpret the concept of "dominance" as a "get him before he gets you" regime and seem to just use that as an excuse for punishing the poor dog. One wonders what their motivation for getting a dog in the first place actually was, because it sure doesn't seem to be about companionship.
Well, notwithstanding all that, here's an extremely good article about teaching bite inhibition. The author has some serious qualifications in dog behaviour, and is someone whose advice is very much worth taking:
http://www.jersey.net/~mountaindog/berner1/bitestop.htm
As you'll see quickly, bite inhibition is NOT about dominance, alphas or any of that punitive
nonsense. It is a learning process with a definitive aim - the dog's understanding of his power and the incredible fragility of human skin. I'd put my trust in a dog taught properly any day over one just pounded on and prevented from using his jaws at all.
If you haven't come across these before (they've been linked many times from this site), then you may find the following articles very useful. LOL - your friend might also find them useful, even something of an eye opener:
Debunking the Dominance Myth, by Pamela Buitrago
The Macho Myth, by Ian Dunbar
The History and Misconceptions of Dominance Theory, by Melissa Alexander
Social Hierarchies, by Ian Dunbar
Why Can't a Dog Be More Like a Dog?, by Ian Dunbar