I have been a practicing martial artist for over a dozen years and have been kicked in the junk a number of times. Yes, it really does suck, but I believe there is a method that helps. I haven't tried the other remedies list above, but this one is quite different. What you do is bounce on your heels. You go up on your toes and quickly drop onto your heels a number of times in a rapid succesion. If it doesn't help at least you will be distracted for a little while.