Are you goddamn kidding me?! My entire childhood revolved around the idea that I knew what to do if somebody at the beach was stung by a jellyfish. I'll tell you what not to do; PEE ON IT!
This... this is exactly why people say they're terrified of the ocean. One day you're sunbathing and walking the shore line with your family, the next you're running into a 5 foot wide, lion's mane jellyfish lurking a bit too close for comfort.