Easy "Out Of Your Depth" achievement

Sharks spawn randomly in deep water. Go out into the ocean with a boat or jet ski, and watch the mini-map until it turns completely dark blue. Keep driving around until you see a red dot on the radar, which indicates a shark. Then, jump into the water, and wait until it kills you. It may take some time if the shark does not see you right away. Once you have been killed by the shark, you will get the "Out Of Your Depth" achievement. Additionally, sometimes the shark will even attack and destroy the boat or jet ski, which will also give you the achievement.