I would agree that for unpredicability, bull sharks are up there. However, there are probably more shark attacks by nurse sharks on divers. They are so docile that it is tempting to touch them. There is even one place I lobster where there are always 2 or 3 large nurse sharks in the same hole as the lobster.
Sometimes you have to "tickle" the sharks out. This particular area is made up of a pile of old empty concrete sewer pipe, stacked about 20 feet high. It's dark inside and the corals are open even in the day.
Unfortunately, if you move the shark to get the lobster, sometimes they turn and go out the way you've gone in. I've actually had them swim under me and can feel them slide past. Still have the family jewels. If you've ever had a moray eel swim through your BC it's the same thing. You just stay real still and usually, nothing happens but a rush when it's over.
If you grab a nurse shark and tug it's tail it will turn and bite. It usually locks on. I've tossed little ones into my lobster bag when I was younger and more stupid. It took a screwdriver and a pliers to get the mouth off the bag. When we let it go it turned and nipped the boat.
I've encountered makos while spearfishing and let me tell you, it's the spitting image of a great white except smaller and stubbier. Luckly we looked at each other and swam off in opposite directions.
I've had several bull shark encounters. They are sneaky. They will come up from behind or they will hang at the edge of visibility until they are ready.
My worst encounter was in Bimini. I ran into a 14 foot Great Hammerhead. It was nearly 3 feet from eye to eye. I was right next to the boat spearing fish. I handed the line to my buddy on the boat and he began to pull up the speared fish. The hammerhead started up too--in an aggressive posture. Needless to say, I started to pull the line down into the water to get the fish and shark away from me. My buddy on the boat wanted to know why I was pulling the line INTO the water. Try saying shark through a snorkel!
Then, my buddy offered me...ready for this...a speargun. What the heck was I gonna do to a 14 foot pi**ed off shark with a speargun?! I just wanted to be out of the water! But I also realized that I couldn't get out of the water fast enough without thrashing to avoid attracting that shark. So I just relaxed, let the speared fish sink to the bottom. The shark picked up the fish and swam away spear and all.
If any of you saw the latest Shark Week, this week on Discovery, you saw one of my dive buddies. Kent. He lost 80% of his calf to a bull shark in the Bahamas. The dramatization was factual and the wound was horrendous. The bull shark missed his artery by 1/8th of an inch. He really does get back into the water at Walker's Cay with 9 bull sharks 3 months later.
In nearly every attack or aggressive encounter, the diver manages to do something provocative to the shark. We are the strangers in this world. You should respect sharks but not necessarily fear them and try not to do the same stupid stuff I've done in my youth. Notice that in every one of my more serious encounters, I have been spearfishing, blood in the water or thrashing fish.
When I have seen sharks when I'm not spearfishing, they just keep on cruising.
Larry Stein
Then I thought: I guess we're gonna find out!! 
