What you call "Jock Itch" is a mycosis, that is a fungus infection. It can affect other parts of the body, mostly wet and humid areas (armpits for example). Very obese people also have a tendency to develop that condition, in the interstices of their body fat.
What your friend needs is an anti-mycosis ointment. The real effective ones are prescribed by doctors and the treatment is quite cheap, usually less than $15, at least here in Canada. Please don't believe in some of the tricks you've read here. Some times the infection gets a bit more complicated and it requires a drug treatment. Overall it's a benign condition that will heal very well if treated appropriately and in time.
Never let the facts get in the way of a good theory.