UFC's Paige VanZant -- Bikini Showdown ... At 'Fight Night' Weigh In

UFC badass Paige VanZant stripped down to her hot pink bikini ... and got face-to-face with Felice Herrig moments ago ... for some half-naked smack talk before they square off tomorrow.

It all went down in New Jersey -- where the women will battle it out in the octagon at "UFC Fight Night" on FOX.

Both women weighed in at 115 lbs ... both are 5'4" ... and both have insane physiques.