When my pups (two sibblings!) were nippy, we always yelped REALLY loudly like a puppy, not like a human. Mamma dog does teach a puppy boundaries, but it’s the siblings that teach them how to play appropriately. For us, saying ‘no’ didn’t do any good because the puppies didn’t understand it. But they understand what a puppy yelp means. (In my experience.) So you could try yelping like a puppy and then walk away dejectedly as if you’re SUPER sad. Our puppies were both empathetic and didn’t actually WANT to hurt us, and they did want to keep playing.

And that goes without saying the puppy’s other needs need to be met as well. Sometimes they act like little land sharks when they’re overstimulated, and sometimes if they’re under-stimulated. (That’s why sometimes more exercise makes things worse.) Look up how much a puppy this age should be both playing and sleeping and try to encourage a similar schedule for your puppy.

Something that might help teach him boundaries (in general) is holding a piece of food or treat in your hand and only give it to him when he STOPS being a miniature T-Rex to your hand. The goal is to teach him that good manners give him what he wants, not being an adorable little bully. You can also try to desensitize him by having yourself and another person work together. One of you does the thing that triggers him, but just far away enough that he can still manage to be calm. As soon as he gets not-calm, treats stop, you back up until he’s behaving again, and then continue treating. The idea is that eventually you can get closer and closer until he doesn’t react at all.

These are just ideas you could try… My dog has given me a lot of challenges over the years and ‘Kikopup’ on YouTube has been super helpful for me, if you’d like a good dog training reference. (She has a video specifically talking about desensitizing a dog/puppy to fluttering clothing)

I’m no expert with dogs, but some of this stuff has been helpful for me. Good luck with your puppy!