Former Cosatu general secretary Zwelinzima Vavi and EFF leader Julius Malema are plotting to overthr.
The 79-year-old star called the 24-year-old singer an "idiot" after watching her open up about ex Chris Brown to Oprah Winfrey.
E!'s 'Fashion Police' presenter tweeted: "Rihanna confessed to Oprah Winfrey that she still loves Chris Brown. Idiot! Now it's my turn to slap her."
Rihanna quickly responded: "Wow, you really do get slow when you're old, huh?"
But it appears she has since deleted the tweet.
In candid interview on 'Oprah's Next Chapter' recently, Rihanna said she still has feelings for ex - even after he was arrested for physically assaulting her in February 2009.
She told the 58-year-old interviewer: "We love each other and we probably always will, and that's not anything that we're going to try to change.
"I think he was the love of my life. He was my first love and I see that he loved me the same way. I truly love him. The main thing for me is he's at peace. I'm not at peace if he's not happy or he's still lonely. I care. It actually matters that he finds that peace."
Joan used the micro-blogging website again to express some advice for the 'We Found Love' hitmaker before inviting her to appear on her own show.
She warned: "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'!"