The feud ended with Hilton, 33, kicking the 28-year-old former 'Nickelodeon' star out of her VIP area, reported New York Post.
Bynes apparently turned up at a restaurant with a male friend, who was wearing a floral headband, and tried to sit at Paris' table, where Hollywood scion Brandon Davis was already holding court.
"Amanda tried to sit at Paris and Brandon's table, and they were not happy about it. There was a scene, and words exchanged, before they kicked her out of their area," a witness said.
"Amanda wasn't drinking, but she was acting really weird. She stood in the middle of the club with her friend, looking really awkward, and just seemed totally out of it," the witness added.
Bynes has reportedly been diagnosed with bipolar disorder and was released from a psychiatric facility on October 30.
Her parents were awarded a temporary conservatorship over the actress after her erratic behaviour spiralled out of control following her DUI arrest earlier this year.