Hi Leahloo,
I have a guppy-mouth terrier who likes to do the same thing as you describe. Over the years, I've learned to hold the treat as if it's a cigarette being protected from the wind. If the dog gets grabby, I twist so the nose hits my knuckles instead of the actual treat. Instead of a treat, a soft rap occurs. At the same time, I say "Hey! -- Gently".
Sure enough, Samma will ease off and go for it when I tell her it's "ok" much more softly the next time. I can sometimes see the gears churning in her head --- kind of an "Oops, I messed up" realization :rolleyes:
For her, it's nothing to do with not "respecting" me ... usually it's because she's excited and just not thinking. She's also a small dog, which sometimes, the hand is held slightly too high for her to comfortably reach, so she's pushing up to get higher.
With my old lab/gsd mix, I did the same thing. In fact, that's where I started this 'style'. He learned fairly quickly not to be so grabby.
good luck with your puppy
toodles