I was stung by some form of jellyfish once before, but did not have the opportunity to try any of the suggested treatments before the irritation went away. I have always heard and was taught vinegar was the way to go as well, and personall would still give that a shot based on other people's experience. For what it is worth, this is from an article I saw the other day:
Dec 2006
Hot water is the most effective way to relieve the pain of a jellyfish sting, a new study has found.
Doctors and medical students at Busselton Hospital in Western Australia purposefully stung themselves with jellyfish to compare four popular treatments - ice, vinegar, aluminium sulphate and hot water.
"Hot water was the only successful treatment, relieving 88 per cent of the pain," the team wrote in the latest Medical Journal of Australia.
"Other treatments were incomplete and temporary."
They said that sting patients treated with hot water at about 45 degrees celsius got "significant" pain relief in 4-10 minutes, and the heat also appeared to stop inflammation.
"There is an urgent need for knowledge of this simple remedy to be spread," said study author, Dr John Taylor.
"And there is the potential that it could even be lifesaving when used with more serious jellyfish stings in the north of Australia."