Katy Perry needs a "liver transplant" after partying with Rihanna

Katy Perry hits Las Vegas with Rihanna for bachelorette bash.. Katy Perry needs a “liver transplant” after partying with Rihanna for her bachelorette bash. The ‘I Kissed a Girl’ singer ‘ who is engaged to Russell Brand ‘ enjoyed a “risque” night with around 25 female friends in Las Vegas last Saturday night , including her pop star pal, ahead of her upcoming wedding ceremony. She tweeted yesterday morning : “Signing up for a liver transplant now.” According to our source, the group wore ‘typical risque bachelorette-themed party items’ ‘ with Katy wearing a hat and veil with the word “Bride” attached – as they enjoyed food and drinks at the Casino Tower and the Hard Rock Hotel and Casino. The women then jumped into a stretch limousine and were driven to the MGM Grand, where they watched a performance of Ka by Cirque du Soleil.   After posing with the show’s dramatically-dressed gymnasts, the group returned to Katy’s hotel suite where they continued the party in private.  The 25-year-old beauty was even presented with an “erotic” cake to celebrate her last few weeks as a singleton. Reminiscing back over the weekend, Katy wrote on twitter “That’s what you get for waking up in…”, a lyric from her hit single ‘Waking Up in Vegas’. It has been a hectic few days for Katy, after her fiance Russell was arrested at Los Angeles International airport last  Friday  after attacking a paparazzi photographer for allegedly trying to take an intimate photo of her. Russell was handed the misdemeanour charge of simple battery.  Discussing the event on twitter, Katy wrote: “If you cross the line & try an put a lens up my dress, my fiance will do his job & protect me.