REMEMBERING the words to his hit songs is not one of Bobby Brown‘s prerogatives. Before the rapper was scheduled to perform at Stereo by the Shore in the Hamptons Saturday night, he partook in a 30-minute make-out session with girlfriend Alicia Etheridge – a longtime friend of his ex, Whitney Hous ton – in the back of a truck. When Brown finally stopped sucking face to sing “My Pre rogative” onstage, one on looker told us, “he stopped singing after the second verse.” Brown then told the crowd, “Sorry, I forgot the words.” Snickering guests included Anna Anisimova and Alessandra Ambrosio.