The meanest, most dangerous dog I knew was an american eskimo owned by my ex wife. This was a 20 pound fluffball, and he looked like he would be friendly and fun to scratch behind the ears.

He loved to bite people, especially children. He had a specific thing he would do when someone looked at him: he would look up and smile, while vigorously wagging his poofy tail. You'd reach down to pet that brilliant white, angel-soft fur, and as soon as you were close enough, he would take a chunk out of your hand or arm. This wasn't a playful bite, he would bite down hard and hang on.