For one, stop trying to scrape away the tentacles. Jellyfish nematocysts are triggered in part by pressure, so pressing on them just prompts them to release more venom. You'll ultimately end up with fewer stingers in your skin than you would if you pulled out the lances with tweezers, but the venom is what really stings—and what could potentially kill you. If you're stung by a box jellyfish, scraping the tentacles away could actually prove fatal. They're highly lethal, and forcing them to release even incremental amounts of additional toxin could spell the difference between I-need-severe-pain-killers and welcome-to-my-funeral. And even if you're just stung by the average, non-lethal jellyfish, you definitely don't want any more poison in you than is absolutely necessary.