I know, I know: I tend to overdo it with the Rihanna postings. But which would your eyeballs prefer? Something about the Republican convention or something about my favorite Hot Mess? So: Did you know that Joker-faced comic Joan Rivers and party-hearty girl Rihanna have been skirmishing on Twitter? In the latest salvo, Joan referred to Rihanna’s ex Chris Brown when she tweeted: “Honey, Rihanna, everyone knows: If he hit you once, he’ll hit you again. Read the statistics. PS — love to have you on ‘Fashion Police.”‘ Joan, of course, mauls celebrities for a living.