Justin Bieber Come Back To Ruins But Keep Your Pantalones On!

EXCLUSIVE

0108-justin-bieber-ruins-TMZ-GETTY-01Justin Bieber has the verde light to return to the Mayan ruins in Tulum, Mexico as long as he "behaves well," or as we say in this country ... don't act like a jerk!

The director for the National Institute of Anthropology and History tells TMZ, Bieber is welcome back -- and doesn't even have to apologize for disrespecting the sacred ground by drinking beer and mooning the tourists.

We're told the only caveat is he better behave and respect the rules that every tourist has to follow. Y'know, things like ... keeping your pants on.