The pit bull, German shepherd and rottweiler are some of the meanest-looking dog breeds. The general physical traits of dogs that make them appear mean are large size, muscular bodies and large heads.
Packed with lean muscle and extremely powerful jaws, pit bulls tend to secure the top position as meanest-looking dog. Their popularity in illegal dog fighting also lends to their generally fearsome air. German shepherds and doberman pinschers are very intelligent and highly trainable, but can be aggressive. Their potential for aggression combined with their general size and air of confidence makes them intimidating. Similarly, rottweilers can be frightening, due to their densely-packed muscles and confident carriage.
The world's tallest dog, the great Dane, can look mean due to its sheer size. Bulldogs have heavy muscular frames and very large jaws, which make them look scary, despite their generally pleasant dispositions and tendency towards laziness. People are often leery of bull terriers because of their unusually-shaped heads and lean, muscular bodies.
Although some dog breeds may look mean, their dispositions may not match their appearance. The reverse is also true, with some sweet, cuddly-looking dogs, such as chows, having the potential for very aggressive behavior. Despite their appearances, all dogs breeds can be raised to be gentle and pleasant if they are properly trained and socialized.