The `I Kissed a Girl` singer - who is engaged to Russell Brand - enjoyed a "risque" night with around 25 female friends in Las Vegas on 18.09.10, including her pop star pal, ahead of her upcoming wedding ceremony.
She tweeted yesterday morning (19.09.10): "Signing up for a liver transplant now."
According to OKmagazine.com, 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 on Friday (17.09.10) 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. #standbyyourman #don`tf**kwiththeBrands (sic)"