Justin Bieber gave us a gift yesterday ... shirtless hiking -- a gift to the world!

The Biebs was with a pal, working up a sweat on the side of the mountain as he stretched and showed off some impressive yoga moves, flaunting his flexibility. The mustache, the Fear of God cap, the saggy shorts with Calvin Kleins ... we just can't.

And then it got even better -- we're seriously not sure what's hotter -- Justin or his new PINK Lamborghini Urus SUV! Actually, Justin wins :)