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Simon Cowell has seen a lot of bad performances in his day.

What stands out after all these years? Clay Aiken's rendition of Grease.

"It was abysmal!" he said Wednesday on Ryan Seacrest's KIIS-FM radio show. "I remember saying on the night, 'You sound terrible, you look awful!' Two years later, he came into my dressing room with a puppy still really, really upset. But I think, and I've said this before in an interview, the performance I liked best was when Fantasia sang 'Summertime.'"

Tonight, Cowell, 50, will end his eight-year stint as the tart-tongued judge.

"It never occurred to me until Crystal [Bowersox] mentioned it at the end [Tuesday's program]," he said. "Then I suddenly remembered, 'Gosh, this is my last night.'"

How does he want to go out?

With some music, of course.

He said he wants to hear "Hero" by Enrique Iglesias or "Hero" by Mariah Carey. Jokes Cowell, "There are two choices."

Cowell -- who will serve as judge and producer on Fox's The X Factor in 2011 -- said he'll miss fellow judge Randy Jackson the most.

"What I love about Randy is he's always in a good mood, genuinely," he said. "If it wasn't for him, I think we would've gone nuts three or four years ago."