Off the top of my head, it's possibly a partial myth. Although they do have suits you can wear to protect against Jelly Fish stings. Clearly barrier protection

Off the top of my head, it's possibly a partial myth. Although they do have suits you can wear to protect against Jelly Fish stings. Clearly barrier protection is effective. So I suppose the myth portion comes from the efficacy of different types of stockings. Fishnets probably dont do much good.... Super thick ones of a quality material probably do work! I'm not sure of the sting mechanism of jellyfish and what level of barrier protection would work.