Bynes and Rihanna had the unpleasant exchange of words on micro-blogging site Twitter.
"@rihanna Chris brown beat you because you’re not pretty enough,” Bynes tweeted to the "Umbrella" singer.
“No one wants to be your lover so you call everyone and their mother that I almost named my dog Rihanna," added Bynes.
To that, Rihanna replied: “Ya see what happens when they cancel intervention?”
This angered Bynes further, and she wrote back: “Unlike your fugly faced self, I don’t do drugs! You need the intervention dog! I met your ugly face in person! You aren’t pretty you know it!”
Later, Bynes deleted those tweets.