Justin Bieber -- Calvin Klein's Happy Trail of LIES!!!

Forget, "When a boy becomes a man." We know what Calvin Klein does when he doesn't.

Check out Justin Bieber's wisp of a happy trail in the pic from the raw video of the photo shoot. Now check out the photo taken for the print ad ... seems like Justin got a digital pelvic merkin.

It's ironic ... CK is trying to make Biebs look more like a man, after being slammed for years for using hairless, nubile young models.