For someone whose made a career out of poking fun at celebrities, Perez Hilton sure has a lot of famous friends. Christina Aguilera sang Happy Birthday to the popular blogger during his 31st birthday bash at The Viper Room in West Hollywood on Saturday night.

Kim Kardashian, Amanda Bynes, and of course, Paris Hilton, were on-hand to ring in Perez’ B-Day in style.

Here’s a video of Christina Aguilera channeling her inner Marilyn Monroe for a performance of “Happy Birthday, Mr. Per-ez-ident.”

Spotted@