i like to compare diving with "dangerous" marine life to visiting the dog park with my dog. when you first arive there are some dogs that come a check you out, others keep their distance. can a dog bite you? yes, but it's not likely. now, if i were to open up a big bag of food and stand in the middle of a bunch of dogs, aggressive or not, i might accidentally get bitten. also, if a pit bull comes on the scene, i'm not going to ru naway like prey, but i'll certainly keeps tabs on where it is.
i have about 150 dices under my belt, and most of them have been with sharks like hammerheads, reef sharks, tiger sharks ,lemon sharks (cocos island, tiger beach, bahammas, etc). my sense is that they just see divers as another big predator. stay out of their way if they want food and you'll be fine. most of the time (hammerhead esp) the sharks are hard to get close to. that being said, i've never seen a bull shark, and wouldn't care if i never do.