Here's Joakim Noah proving he's got nothing to hide when it comes to getting naked -- stripping off his pants in the middle of the street in Santa Monica ... and yeah, dude's in great shape.

The New York Knicks player was leaving a vintage French boutique in Santa Monica on Monday -- when he decided it was time for a wardrobe change.

Off came the shorts ... out came his bare ass -- and Noah couldn't help but smile as people walked by him in the middle of the day.

Joakim Noah's 6'11", 230 pounds and was standing in front of his expensive Porsche ... so, we're sure no one even noticed -- right?