Usually I have to advise users on how to keep their G-fit tight on the end of the pole!
As has been said metal on metal can cause quite a tight fit, so the best way of undoing this would be to get one person to hold the poles top section tightly and then if you 'wobble' the gooseneck back and forth whilst trying to unscrew it, this will allow a little movement on the thread which will enable you to unscrew it little by little.