Rihanna in Twitter Feud With ... Joan Rivers

Joan Rivers likes to pick fights on Twitter, and this time she's engaged Rihanna. Rivers called Rihanna an "idiot" and said she wanted to "slap her" after the singer told Oprah Winfrey she still loves Chris Brown. Rihanna's first response, which she ultimately deleted: "wow u really do get slow when you're old huh?" Later, she tweeted "Slap on some diapers." (That one remains up, E! reports.)

Rivers was unfazed, replying, "Honey, @Rihanna, everyone knows: If he hit you once, he'll hit you again. Read the statistics." She ended with an invitation—one we have to imagine will be ignored—for Rihanna to appear on Fashion Police. Rivers may be happy to hear that Rihanna has apparently moved on: The Daily Mail reports that she was spotted Saturday night going go-karting with ... Rob Kardashian.