A family friend had a St. Bernard as their dog for a number of years. They purchased said dog as a puppy. For some reason they allowed the dog to believe that walking between a person's legs was an acceptable way to greet people and gain pets. Nothing like having a >200lbs dog force his way between your legs and momentarily lift you off the ground to absolutely scare the shit out of you in its misconstrued gesture of joy and acceptance. Aside from this behavior the dog was nothing short of proper loving and caring.

I'd also like to say that it seems that people with bigger dogs seem more likely to properly train them. People with smaller dogs seem to think they don't have to put in the same amount of work and end up with nippy, shit behaved dogs.