Happily single Paris Hilton partied at Villa with Avril Lavigne… until Benji, Joel, and Nicole Richie showed up… then they took off and met up with her sister Nicky and went back to Nicky’s house for the after party…

Apparently Avril and her rocker husband Deryck Whibley are also having issues… maybe they are BUBs?  That’s Break Up Buddies for those of you who don’t read Cosmo!

I have always found it odd that once in a while Paris and Avril hang out.  Avril just seems like she’d be so anti-Paris Hilton, but I guess not.

Photos: Splash News Online