1. Olivia Newton John as "Olivia Newton John"
I've never been at all impressed by this actresses ability; even in Grease, her most famous role (incidentally the focus of the next two episodes of Glee to air) she was incredibly poor on the acting side of things. However, the reason she grabs the top spot of Glee's worst ever guest stars is because both the times the character appears it is for unbelievably unrealistic and stupid reasons. Despite not really doing anything significant in the last 30 years, the actress is still world famous and the idea that she would travel to Ohio in order to judge a singing competitions Regional stages (not even the finals in National which would be a little more realistic) is ludicrous- but this isn't the worst of it. Her first appearance on the show has Olivia Newton John phone up Sue Sylvester in order for her to star in a new music video with her of her song "Physical" because the Glee kids put a video of Sue online showing her dancing to the song. I know most of what happens in Glee doesn't happen in real life but I am still going to say this here: "THIS DOESN'T HAPPEN IN REAL LIFE". This was for me the biggest roll your eyes moment the show has ever had, and for all those that think the show has gotten worse in Season 2, 3 and 4, you should only cast your mind back to appearances and episodes like this one. Any celebrity I missed out on either the good side or bad side of things. Be sure to give me your opinions in the comments section below...