I know the white or translucent ones I see are safe, or relatively safe, but this red one, found in Cheongcho Lake, just looks dangerous. Most of the jellyfish I see have been pounded by surf along shore and have probably already fired their cnematocysts (I am not sure about the spelling but I mean the poison darts carried in their tentacles); this one looks hale and ready for trouble.
Melissa asked about the jellyfish that Koreans eat and I have no idea what kind is eaten. I once bought Hae-pari mustard with bits of jellyfish in it, but again, I don't know what kind it was.
By the way, Pari can mean 'insect' in Korean. Is haepari (해파리) 'ocean insect'?
Click on the images to enlarge.