R&B singer Chris Brown has taken down his Twitter account after a vulgar online exchange with comedian Jenny Johnson.

Johnson says she's now receiving death threats on Twitter from Brown's supporters.

The fight started when 23-year-old Brown posted a picture of himself, saying he looked old. Johnson replied: "I know! Being a worthless piece of (expletive) can really age a person."

Brown fired back a series of crude sexual jokes. Johnson posted a link to a news story about Brown's 2009 assault on singer Rihanna.

Before deleting his account, Brown wrote: "Just ask Rihanna if she mad??????" The on-again-off-again couple have been seen together recently.

A representative for Brown's record label didn't immediately respond Monday to an email seeking comment.

Brown had 11.6 million followers on Twitter.

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Online:

http://www.twitter.com/JennyJohnsonHi5