Justin Bieber fielded an unusual request from a passenger on an international flight — and it went something like this: shut your expletive-filled pie hole! Please. It all happened during the Biebs’ return from a Down Under promotional tour. Sources on the 12-hour Air New Zealand flight last weekend … tell us JB was surrounded by his entourage in first class when things started getting out of hand. We’re told 18-year-old Justin and his posse were blurting out cuss words — including some 4-letter selections — and getting so loud … a female passenger finally stepped to Bieber. We’re told the woman … a mother of 2 … walked over and asked Justin to “stop yelling curse words and using that kind of language on a plane. It’s not appropriate.” A source close to Justin tells us he was completely embarrassed, quickly apologized to the woma. TMZ