From Rollingstone.com

Slash has told Entertainment Weekly that he rejected a request from the producers of Glee to use Guns N’ Roses music in an episode of the series. His reasoning was pretty simple: He thinks the hit show is horrible. “Glee is worse than Grease and Grease is bad enough,” he told EW. “I look at Grease now and think, ‘Between High School Musical and Glee, Grease was a work of art.'” So Slash is definitely not a fan of squeaky-clean singing teens. I’ve been a huge fan of Slash up until this moment and now…I just love him even more. Go Slash.