Trick or treat?

Rihanna dresses up as a sexy tiger while posing with glamour model Coco at a Halloween party at M2 Ultra Lounge in the Chelsea neighborhood of New York City. The Halloween party was hosted my Mariah Carey and her husband Nick Cannon.

Gossip Girl co-star Blake Lively, 22, was dressed up as a sexy flight attendant while boyfriend Penn Badgely was also around dressed as a geek

Adam Lambert dresses up as a glammed-out vampire. All night, the newly single American Idol vet was seen hanging out with pop rock singer Ferras, who dressed up as an Arabian Prince with Markus Molinari.

Mickey Rourke looks ghostly as he leaves a Hollywood nightclub.u00a0 The 57-year-old Wrestler actor stepped out for a Halloween celebration in this get-up u2014 he looks like his own version of The Joker, right?

Kelly Clarkson dresses up as Family Guy's Stewie Griffin during her Halloween Concert at the Family Arena

Zachary Quinto is the walking dead as a sexy skeleton at celebrity photographer Tyler Shields' Halloween Party at his home