'American Idol' — Mocking Simon Cowell Behind the Scenes

Simon Cowell is the butt of an inside joke behind the scenes at “American Idol” … and it”s all over some cocky statements he made about a rival show just a couple of months ago.

Sources at “Idol” tell us … the honchos have been joking that they”ll be DEVASTATED if the show doesn”t get 20 MILLION viewers when “A.I.” debuts tonight.

They”re not serious … they”re simply mocking their former judge, who told the Hollywood Reporter last year he was counting on “X Factor” to pull in 20 mil on its debut … or else he”d consider it a disappointment.

For the record, X Factor fell short. But “Idol” has hit the 20 million mark multiple times … including the 2011 finale.

Maybe the “A.I.” guys aren”t joking after all …