I think it is a territory thing. Our weimaraner used to go to work with my huaband and basically lived in the van, when it was parked outside work he would leave the tailgate open and Max was on a long rope so he could have a little wander round or just be in his basket in the van. He had the life of Riley, as it was opposite a bakery and their customers used to bring him pies etc (the dog, not hubby!). However one day a lady who had met him before but on neutral ground, leaned in the back of the van to say hello, and he went bonkers and leapt at her, snapping and snarling, which was pretty out of character for him. This was the only time he ever did anything like this with a human being, so can only think it was a case of guarding his territory (though he did sleep through a burglary, and would not investigate noises outside if it was dark, unless we went first!!).
You can't blame the dogs, I would'nt stick my head or hand into a car with a dog in, would you??! :roll: