As Spoungbob was walking home from the Krusty Krab he noticed a B-22 Bomber in the sand. So he took it up for a spin (even though there was a nuclear bomb in it.) Meanwhile Mrs. Puff was walking below him. Then Spoungbob hit the RED button which he thought was the air conditioning, which conveniently was the button that dropped the nuclear bomb.
So the bomb exploded on Mrs. Puff & ended life in the sea. So the $ 500,000,000,000 B-22 bomber crashed. But Patrick was under his rock at the time which created a safe spot. So he walked outside and got radiation sickness and died. After that the world blew up.