1. Lindsay Lohan vs. Avril Lavigne
It all started when Avril Lavigne failed to speak to Lindsay Lohan at the Chateau Marmont, supposedly because she just didn't see her. Lilo took it as a major snub, and when Avril tried to correct her mistake and make nice, Lohan wasn't having it. Sources say when they saw each other later, it was Avril who snubbed Lindsay -- and Lindsay tried to get her thrown out of the bar. Security refused.