John Mayer Says Hello to 40 in PJs and $600 Sandals!!!

John Mayer is now 40 and supremely confident in his wardrobe choices ... and he flaunted it as he stepped off a plane in Rio.

John arrived in Brazil Monday -- the day he hit the big 4-0 -- to do 5 concert dates. Fans greeting him in the airport got some serious eye candy courtesy of John's floral patterned pajamas or scrubs (we really can't tell) ... and his bright red sandals.

Before you start thinking Mayer's giving up in his 40's ... we should tell you those sandals are Visvim Christos, and they go for about $600!