The red-haired superstar - who has over 3 million followers on the social networking site - Tweeted in reply to a post from her rapper pal Katt Williams.
'Watchin clifford the big red dog =) somehow im reminded of @Rihanna idk (I don't know) why tho,' Katt posted.
Rihanna, 22, wrote in reply: 'LMAO (Laughing my arse off), Katt u lil c*nt.'
'Rihanna is a role model to millions of young, impressionable kids,' a devotee tells the Sun.
'She shouldn't be using that kind of language - especially when she knows how many people follow her.'
The hot-headed superstar is not the only showbiz personality to use the C-word in a Tweet.
Kelly Osbourne (637,690 followers on Miss Kelly O) called ex Luke Worrall a 'using C*nt' in a Christmas Twitter rant that was later deleted.
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