A couple of veterinarians told me, one way to break a dog who wolfs stuff out of your hands or grabs other peoples stuff is hold out your hand in a sure gesture of 'it's for you bowser' and have a golf ball size blob of peanut butter in your hand. Most dogs won't be able to swallow it and end up in the comedy routine of head rolls and tongue shenanigans.
Has to be repeated a few times and you should see the dog start looking at your hand. Even if they like peanut butter. If after some time they start grabbing again, just do the same routine a handful of times. The vets said almost all dogs get the hint at some point.