The ones that'll kill a human are called [box jellyfish](https://en.m.wikipedia.org/wiki/Box_jellyfish), and you can forget your vinegar if one gets you!

And on Australian beaches, if you're stung by the more common "blue bottle" jellyfish for instance, you don't need vinegar handy, you just get your mate (or a random stranger) to pee on it. No, seriously, urine will help sooth the sting... unless it's from box jelly, then your a goner, but they're only common in the northern tropical waters of Australia, where you've got other BIG things to worry about, like saltwater crocodiles! Now there's a man eater!