10 Most Aggressive Dog Breeds: Temperament Ratings and Information Looking to Adopt? Are you are looking to get a new puppy to keep as a family pet and would like to know which breeds may not be the safest for children? In doing this research, I found that different organizations and “experts” have differing opinions as to which dog breeds are the “most aggressive,” so below, I've listed the 10 that most sources seem to agree on. How Canine Aggression Is Defined Dog aggression is typically defined as dangerous behavior directed at another individual (like a human or another dog). Aggressive behaviors include barking, biting, lunging, snarling, etc. The causes of these behaviors can range from territorial defensiveness and protectiveness to fear and social anxiety. How I Determined Which Dog Breeds Are the Most Dangerous. The 10 breeds listed below had some of the lowest overall passing rates in conducted by the American Temperament Test Society and are sorted in order from ...