The singer then mumbled and slurred through a performance of 'Just Friends'. The singer seemed confused while adjusting her shoes, before taking one of them off and walking over to the microphone. She appeared to stumble onto the stage before hugging one of her guitarists. Winehouse checked out of rehab last month in order to begin her European tour, but she was booed when she took to the stage an hour late. Amy Winehouse has been booed during a concert in Belgrade, after frustrated fans watched the singer appear lost and incoherent.