An elderly man opened fire on fans at a Senegal rap concert he believed were making fun of him by singing a song about cranky old men, police say.The 70-year-old began shooting with a hunting rifle at Lobaly village in the Matam region at the weekend.Police say the gunman warned fans to stop singing "Pa' Tang Xol" (Angry Old Men) by popular Senegalese artist Baaba Mal before opening fire.