Chris Hemsworth and Matt Damon Double Date at the Beach

Chris Hemsworth is teaching Matt Damon what it means to be a true beach dude, Down Under, and lesson number one appears to be ... ditch the shirt, bro!

Matt and his wife, Luciana Barroso, have been hanging with Chris and his missus, Elsa Pataky, all week down in Byron Bay, Australia. Wednesday was a beach day -- the wives were rocking bikinis while Chris, Matt and another friend checked out the surf.

Check out the pics ... the Damons handled the PDA this time around, although Matt was way more subtle than Chris in that department.

No doubt, this pairing of couples makes for a super fit looking double date, but, c'mon -- hanging next to shirtless Hemsworth can't be easy. We're with ya, Matty!