The starlet gathered family and friends at a beach-front bungalow in Malibu yesterday for her 21st birthday bash, where the paparazzi caught Lindsay hanging with boozey ex Calum Best while dressed only in a bikini and the world’s nastiest pair of bright blue heels. Friends brought pricey gifts for the rehabbing actress, as they snacked and played volleyball while DJ and Lilo pal Samantha Ronson spun records. Fellow sobriety fan DJ AM stopped by, as did her mom Dina (Cartier gift in hand), and Lindsay captured the festivities – and the paps – on her giant camera. The party starting winding down around 2am and Lindsay ended her big day right where she had started it, at Promises Treatment Center. Pure Nightclub – eat your heart out.