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Most vile pickup line ever?

Chris Brown -- who pleaded guilty in 2009 for felony assault for hitting then-girlfriend Rihanna -- confidently approached an attractive brunette Feb. 10 at the Lasio Professional Hair Care suite Grammy gift lounge and asked her, "Can I get your number? I promise I won't beat you!" the woman tells Us Weekly.

"He and his friends laughed, then one yelled, 'That's his new line!' Ugh! I wanted to throw up!"

Counters Brown's rep: "That is absurd and absolutely not true. He did not say that nor would he joke about that."

Though the singer, 22, may randomly flirt with the ladies, Rihanna, 24, is remarkably still in the picture. As Us has reported, several sources say the pair have hooked up over the past year, hanging out as recently as Feb. 9  -- and two insiders reveal they are even recording a single!