Viewers of the "Rosie O'Donnell" show got an eyeful yesterday when an audience member flashed her breasts while the show was on the air live - here and in about dozen markets around the country. The incident occurred near the end of the show, during a routine overhead shot of the crowd. O'Donnell looked shocked, noting that in six years on the air a flashing had never happened. "She is now with security, waiting to get into the 'Montel' show," a flustered O'Donnell told viewers.