Friendliness toward dogs and friendliness toward humans are two completely different things. Some dogs may attack or try to dominate other dogs even if they're love-bugs with people; others would rather play than fight; and some will turn tail and run. Breed isn't the only factor; dogs who lived with their littermates and mother until at least 6 to 8 weeks of age, and who spent lots of time playing with other dogs during puppyhood, are more likely to have good canine social skills.