Your friends logic is flawed in that Superman's powers are the result of his exposure to the yellow sun in our galaxy. As has also been shown something as simple as Kryptonite is able to render him harmless. It is only with the assistance of others, or through mental ingenuity and not physical strength, that he has been able to get out of those situations.
It would not be unusual for Superman to called out with a "I will bring you down to Bacontown!" challenge and lose. Heck, in the Death of Superman comic book series he was actually killed!