The newly single singer hit up
Richard Simmons Matthew Morrison's private bash at Voyeur presented by Onitsuka Tiger dressed as a sexy cop last night.
Xtina came with some of her dancers and enjoyed the live band. Another famous blonde friend of Matthew's was rumored to be there as well, but...
Cameron Diaz didn't attend the party.
"She was dressed as a bird and had trouble drinking with her beak on," an onlooker said.
Meanwhile, other stars danced with the dead over at the Hollywood Forever cemetery, where Maroon 5 hosted their own spooky soiree.
Bacardi-serving bars and a dance floor were set up amongst the graves.
Mischa Barton was also spotted roaming around, although no one could really tell what her costume was. Since she normally dresses pretty scary anyway, maybe she thought she didn't need a disguise?