Rihanna clashed with Ciara when her fellow R&B singer-dancer-hottie dissed her in a TV interview with (guess who?) Joan Rivers, saying, "Rihanna used to be so nice. I ran into her at a party and she wasn't the nicest." Rihanna came right back at Ciara on Twitter: "My bad ci, did I 4get to tip u? #howrudeofme." Ciara replied with her own jab: "Trust me Rihanna u dont want to see me on or off the stage." Rih Rih's retaliation? "U gangsta huh? Haaa. Good luck with bookin that stage u speak of." Ouch! The two later reconciled via, you guessed it, Twitter.