Last year I was wakeboarding in one of the waterways off the bay, was tired, motioned to the boat driver and I dropped the rope. I sank down and was waiting for the boat to come around... right in the middle of about 20 jelly fish. That $hit lit me up!
I have heard the same thing from my lifeguard friends. I use what works for me. Papain, papaya, and meat tenderizer break down the amino acids that are injected by the man o wars. If you are allergic to papaya, you should not use this. I have been hit many times by man o war, and I have found out removing then testicles and getting treatment very quickly is key. That's why I have my first aid in my backpack. By the time you get to a guard tower, or if you are remote, it (the pain) will travel and get intense. If you or some one you are with gets hit under the arm or in other sensitive areas like the neck, call 911.
You are supposed to use sulfuric acid for these wounds. Then, you will feel no pain from the man-o-war!!
I was in Corrolla NC, last century, a couple days after a men o war infestation. There were a load of balloons all broken up on the beach from a big noreastern. The waves were chest to head, glassy and peeling lefts and rights. I went out and felt like I was being electrocuted by the pulverized testicles. I kept telling myself, next wave in. stayed out until I was too hungry to surf.
I got stung on my balls one time. Not sure how the tentacles got up my shorts but it hurt like hell. As I was running to my car someone yelled out to hit it with meat tenderizer. I raced home in agony and ran to the the cooking utensil drawer and grabbed the tenderizer. You know the metal kind with the cross hatch pattern? I just started beating on my ball sack like a prisoner on a chain gang. Surprisingly it worked really well for getting my mind off of the jellyfish sting.