The middle of the goddamn ocean during a storm. When the boat rocks and the entire horizon goes up and away and your faced with a wall of water that was perpendicular to you only a second previous. I don't believe in God but holy fuck did I believe in him then and did I pray to him.
That sounds like one if the scariest things imaginable. I guess all you can do is prey, because you sure as shit have no control over the ocean. Still, though, must be pretty cool to have lived through that and come out OK.