Closest I got to a shark was spear fishing north shore Kauai. Buddy had our fish buoyed on a 50' leash and mr sharky started chowing down on them. Was kind of a scary swim back as we were out 1/4 mile or so. Most of our fish were lost but the swim was awesome.
Not long before shark came along we got a visit by a hawaiian monk seal. I actually started to panic when I saw something huge swimming my way. Kept watching and it straight swam right up on me. Not 10 feet away just slowly checking me out. Cute puppy dog face but sketchy as hell due to it's size. It could have wrecked me if it wanted to.
Fun stuff all around.