The pilot stated that he conducted the preflight checks of his helicopter and everything checked out fine. He started the helicopter and everything was "normal". He picked the helicopter up to a hover and taxied over to the airport's fuel pumps. The pilot brought the rpm back to 1,800 rpm, and put the friction on the cyclic and collective. The pilot stated that his passenger was sitting on the left hand side, and before he got out of the helicopter he asked him not to touch the controls. The pilot proceeded over to the fuel credit card system when he heard a noise. He looked behind him and the helicopter was rolling over on its side. The helicopter hit the ground and the engine stopped. The pilot asked the passenger to switch off the master switch, and then he helped him out of the helicopter. The pilot stated that he would not "Hot Refuel" on his own in the future. The airport manager reported that the pilot has been told many times that "Hot Refueling" was prohibited at this airport. In the airport operation instruction manual section 4.02 Fueling Operations (a.1) states: "No aircraft shall be fueled or de-fueled while one or more of its engines are running or the aircraft is being warmed by external heat".