Another day, another star parties in London and lets their hair down. Or in Emma Watson's case, flashes her Britney to the paparazzi. Joining the very exclusive peek-a-boo sorority helmed by Spears, Lindsay Lohan and Paris Hilton, recently legal Hermione Granger celebrated her 18th birthday by partying across the pond with co-stars in a very demure little black dress, but made the all-too-common mistake of failing to exit her chauffered car in the proper manner. Though it appears the potential bad girl was wearing some kind of thong-ish type thing, her lacey underwear left little to the imagination. And though it's not our place, we do recommend Watson consider heading to the nearest waxer before flashing her nether regions again. A closer look after the jump.Not to get too personal or anything, but when we were 18, we weren't exactly jumping on board the waxing trend either. But we also made sure not to let the whole world know it. But considering Emma's most recent paramour, that shaggy-haired mind-bogglingly gorgeous girl-attracting Razorlight front man Johnny Borrell, Hermione may be determined to grow up faster than her peers. Our only other theory? Harry Potter superstar Daniel Radcliffe has been stealing Emma's thunder for, well, practically her entire life. And now he's set to reveal all on Broadway. Could this be his hotter-by-the-second co-star's way of redirecting the spotlight towards her and her own assets? In any case, we do give the girl credit for covering up, even if "covering up" means pretty much showing us all exactly whether or not the carpet matches the drapes (it does).