John Mayer Scores Diamond 'Big Lebowski' 'The Dude' Chain for 40th Birthday

John Mayer's way over the line with his 40th bday celebration -- 'cause he's hanging with the Dude.

The singer bought an iced out chain pendant of one of his favorite movie characters -- the Dude from "The Big Lebowski." The 18k white gold piece is covered with 41 carats of diamonds. We're told it took IF & Co. Jewelers about 2 months to complete.

Famed celeb jeweler Ben Baller delivered Mayer's gift Monday at LAX. No word on how much John paid, but our sources say it's worth at least 6 figures.

For Mayer, "Anxiety and worry is canceled this week."

We abide.