Selena Gomez didn't pull any strings in Puerto Vallarta ... dammit.
Biebs' former squeeze was showing off the goods during her Mexican vacay ... sporting a double-stringed bikini bottom thingy (we know fashion).
There's not a ton of material to her ensemble, but what there is -- is definitely working overtime to cover the 22-year-old's assets. Things are getting thick down in Mexico.
It's high-season for tourism.