Orca whales are very curious creatures. They often, especially the young ones, like to get dangerously close to humans who are in boats or out for a swim. Or as in the video below, they sometimes like to approach paddle boarders.
It's likely that when they get too close, they just want to say hello, but the experience can still be harrowing -- they are called killer whales, after all. Luckily, this paddle boarder had his GoPro running during the encounter so we can relive the terror with him firsthand.
I don't know about him, but if that had happened to me, I would have been thanking my lucky stars rather than laughing and smiling. Yikes!